Piezoelectric motors and motor driving configurations

ABSTRACT

A piezoelectric motor comprising: a layer of piezoelectric material having narrow edge surfaces and first and second large face surfaces, formed with at least three arms, each extending radially outward from a common central region and terminating in an end; and at least one electrode on the first face surface and at least one electrode on the second face surface.

RELATED APPLICATIONS

The present application is a U.S. national application ofPCT/IL00/00698, filed Oct. 31, 2000.

FIELD OF THE INVENTION

The invention relates to piezoelectric motors and in particular topowering electric shavers with piezoelectric motors.

BACKGROUND OF THE INVENTION

The electric shaver invented by an American, Colonel Jacob Schick, in1928 is one of the most ubiquitous personal hygiene and cosmeticaccessories in today's world. It is a small hand held appliancegenerally comprising a plurality of closely spaced cutting blades havingcutting edges for cutting facial or body hair. The blades are mounted orformed on at least one blade support structure, hereinafter referred toas a “blade head”. A small electric motor is coupled to the at least oneblade head and moves the at least one blade head to impart rapid rotaryor linear oscillatory motion or non-oscillatory rotary motion to thecutting blades. The blade head is mounted in the shaver so that thecutting edges of the cutting blades are located behind a thin perforatedguard plate, generally referred to in the art as a “foil”. The foil ispressed to and moved back and forth along a region of skin to be shaved.Hairs on the region of skin poke through the perforations in the foil asit moves over the skin and are cut off by the cutting edges of therapidly moving cutting blades.

Many companies, among them many international companies whose names arecommon household names are involved in the development, manufacture andmarketing of electric shavers. There is constant ongoing effort by thesecompanies to produce a better electric shaver that gives a better shaveat a lower price.

SUMMARY OF THE INVENTION

An aspect of some embodiments of the present invention relates toproviding an improved shaver in which cutting blades comprised in theshaver are moved by at least one piezoelectric motor.

The cutting blades are mounted on at least one blade head that is formedwith or mechanically coupled to a surface, hereinafter referred to as a“coupling surface”, to which a surface region, hereinafter referred toas a “motor coupling surface”, of at least one piezoelectric motor ispressed. When the piezoelectric motor is turned on, vibrations excitedin the motor coupling surface of the piezoelectric motor transmit motionto the coupling surface and thereby to the cutting blades. Optionally,the surface region of the piezoelectric motor is a surface of “friction”nub formed from a hard wear resistant material such as Alumina,stainless steel or a wear resistant high impact plastic such as PEEK(polyethyl ethyl ketone), that is attached to the piezoelectricvibrator. Optionally, the at least one piezoelectric motor is of a typeor similar to a type described in U.S. Pat. No. 5,616,980 to Zumeris etal, or in PCT Application PCT/IL99/00288 entitled “MultilayerPiezoelectric Motor”, the disclosures of which are incorporated hereinby reference. Piezoelectric motors described in the referenced patentsand PCT application comprise a relatively thin rectangular piezoelectricvibrator having large parallel face surfaces and narrow short and longedge surfaces. A surface region of a short edge of the vibrator or asurface of a friction nub on a short edge of the vibrator functions as amotor coupling surface. Electrodes on the face surfaces of the vibrator,or on face surfaces of layers of the vibrator for piezoelectric motorsdescribed in PCT/IL99/00288, are electrified to excite vibrations in thevibrator and thereby in the motor coupling surface. Generally, twoorthogonal resonant vibration modes, a longitudinal vibration mode and atransverse vibration mode, are excited in the vibrator to providevibrations in the motor coupling surface. The longitudinal andtransverse vibration modes generate vibrations in the motor couplingsurface that are respectively parallel to the long and short edges ofthe vibrator. In some piezoelectric motors of a type described in thereferenced patent and application, a motor coupling surface is locatedon a long edge surface of the vibrator and/or more than one motorcoupling surface is located on an edge surface or surfaces of thevibrator. The motors are mechanically simple, compact, robust motorsthat for a given power requirement, can generally be made smaller thanconventional electric motors such as those used for electric shavers.

In some embodiments of the present invention, the efficiency ofoperation of the at least one piezoelectric motor is improved byenergizing the at least one piezoelectric motor using methods anddriving circuits described in PCT Application PCT/IL99/00520, entitled“Method and Apparatus For Driving Piezoelectric Motors”. In someembodiments of the present invention, holes are made in the body of thepiezoelectric vibrator and/or grooves are made in edge surfaces of thevibrator to optimize the overlap of the excitation curves of vibrationmodes that are excited to generate vibrations in the motor couplingsurface. The optimization of the excitation curves improves theoperating efficiency of the piezoelectric motor. The holes and/orgrooves are located responsive to locations of nodes and antinodes ofthe resonant vibration modes.

According to an aspect of some embodiments of the present invention theat least one piezoelectric motor comprises an electrode configurationthat improves the efficiency of operation of the piezoelectric motor.The electrode configuration comprises a large L shaped electrode on aface surface of the vibrator comprised in the motor that coverssubstantially three-quarters (three quadrants) of the area of the facesurface. Both longitudinal and transverse resonant vibration modes ofthe vibrator are excited when the electrode is electrified. Because ofthe relatively large area of the L electrode, a large volume of thevibrator is excited when the electrode is electrified. As a result,energy is more efficiently coupled into vibration modes of the vibratorthan is coupled into the vibration modes when the vibrator is excitedusing electrodes covering less area of the face surface than the Lshaped electrode.

According to an aspect of some embodiments of the present invention, theat least one piezoelectric motor comprises an asymmetric friction nubmounted on an edge surface of its vibrator. The motor is electrified toexcite a single resonant vibration mode of the vibrator. The excitedvibration mode generates motion of the friction nub along a firstdirection. The asymmetry in the friction nub generates a torque in thebody of the friction nub that generates a bending vibration mode in thebody of the friction nub along a direction orthogonal to the firstdirection. Preferably, the frequency of the bending mode of the frictionnub is close to the frequency of the single resonant vibration modeexcited in the piezoelectric vibrator. The two motions combine totransmit motion to a body to which the piezoelectric motor is coupled.

The asymmetry in the friction nub will generally also generate torque onthe body of the vibrator. In some embodiments of the present inventionthe asymmetry excites a vibration mode of the vibrator. In someembodiments of the present invention dimensions of the vibrator arechosen so that the torque does not excite a vibration mode in thevibrator.

In some embodiments of the present invention a friction nub is locatedso that its center of mass is displaced from an axis of symmetry of thevibrator of the piezoelectric motor. When the motor is operated,electrodes in the vibrator are electrified with an AC voltage to excitea first vibration mode of the vibrator that vibrates the friction nuband mass points in the piezoelectric vibrator along the axis ofsymmetry. Because of the displacement of the friction nub from the axisof symmetry, a second vibration mode of the vibrator is excited thatmoves the friction nub and mass points in the vibrator in a directionperpendicular to the axis of symmetry. The displacement of the frictionnub in effect breaks the symmetry of the vibrator about the axis ofsymmetry and mechanically couples the second vibration mode of thevibrator to the first vibration mode of the vibrator. In accordance withanother embodiment of the present invention the symmetry of thepiezoelectric vibrator is broken by breaking the symmetry of thegeometry of the vibrator, for example by mitering a corner of thevibrator.

If both the first and second vibration modes of the vibrator are excitedby electrifying electrodes in the vibrator with an AC voltage, energymay be more efficiently coupled to the second vibration mode as a resultof the breaking of the symmetry of the vibrator. In addition, theasymmetry will generally preferentially couple energy to particularrelative phase of the second vibration mode with respect to the firstvibration mode. For example the asymmetry might preferentially coupleenergy into transverse and longitudinal vibration modes when they areexcited to generate clockwise elliptical motion in a friction nub ratherthan counterclockwise elliptical motion.

An aspect of some embodiments of the present invention relates toproviding a shaver in which the at least one piezoelectric motor impartsrotary motion to the cutting blades.

In some embodiments of the present invention the shaver comprises atleast one blade head, hereinafter referred to as a “rotary blade head”,comprising an axis of rotation about which it is rotated and a hub towhich cutting blades are connected. In some embodiments of the presentinvention, the cutting edge of each cutting blade extends from a pointat or near the hub in a general radial direction away from the hub.Optionally, a segment of each cutting edge lies in or close to a sameplane perpendicular to the axis of rotation.

In some embodiments of the present invention each blade head is coupledto a circular disc having an axis of rotation coincident with the axisof rotation of the blade head. An annular surface region of the discsubstantially perpendicular to the axis of rotation functions as acoupling surface for the blade head. In some embodiments of the presentinvention the rotary blade head is coupled to or formed with acircularly cylindrical coupling surface having an axis of rotationcoincident with the axis of rotation of the blade head. At least onepiezoelectric motor is coupled to the blade head by resiliently pressinga motor coupling surface, such as, optionally, a surface of a frictionnub, of the piezoelectric motor to the coupling surface of the bladehead. Vibrations excited in the piezoelectric motor rotate thecylindrical coupling surface and thereby the blade head and the cuttingblades attached thereto.

In some embodiments of the present invention, the at least one rotaryblade head comprises a plurality of rotary blade heads having circularlycylindrical coupling surfaces. In some embodiments of the presentinvention, the axes of rotation of the rotary blade heads are parallel.The, intersection points of the axes of rotation with a planeperpendicular to the axes of rotation define a polygon, hereinafterreferred to as a “configuration polygon”. (Note that the polygon becomesdegenerate and reduces to a straight line when there are only two rotaryblade heads.)

In some embodiments of the present invention, at least one piezoelectricmotor is mounted between each pair of adjacent rotary blade heads on theconfiguration polygon. Preferably, the at least one piezoelectric motorcomprises two friction nubs and a different friction nub of the twofriction nubs of the at least one piezoelectric motor contacts thecylindrical coupling surface of each of the two rotary blade head.Preferably, a line between the friction nubs is substantially parallelto a side of the configuration polygon. Each rotary blade head is thuscoupled to at least two piezoelectric motors that lie along adjacentsides of the configuration polygon on opposite sides of the blade head.Preferably, a resilient force urges each coupling surface in a directionalong the bisector of the angle formed by the two adjacent sides of thepolygon on opposite sides of the coupling surface. Preferably allcoupling surfaces are pressed with substantially a same magnitude forceto all surface regions of piezoelectric motors that they contact.Optionally, the configuration polygon is a convex equilateral polygon.When this is the case, the resilient force operating on each couplingsurface urges the coupling surface towards the center of theconfiguration polygon and all the resilient forces have a samemagnitude. (Note, that when there are only two rotary blade heads, andthe polygon degenerates to a straight line, each of the blade heads iscoupled to a same at least one piezoelectric motor that is positionedbetween them.)

When a configuration polygon is a convex equilateral polygon, thepolygon can be inscribed in a circle, hereinafter referred to as a“configuration circle”. In the discussion below, for configurations ofblade heads having a configuration circle, the configuration circle willbe used in specifying features of the configuration.

In some embodiments of the present invention, each rotary blade head onthe configuration polygon is coupled to its own at least onepiezoelectric motor. In some embodiments of the present invention forwhich the blade heads define a configuration circle, the at least onepiezoelectric motor that drives a blade head is positioned and orientedparallel to a radius of the configuration circle. (The radius intersectsthe rotation axis of the blade head.) A resilient force operating on theat least one piezoelectric motor urges the motor in a direction parallelto the radius to press a motor coupling surface of the motor to thecylindrical coupling surface of the rotary blade head. In someembodiments of the present invention a resilient force operates on therotation axis of the blade head and urges the rotation axis towards thecenter of the configuration circle to press the coupling surface to theat least one piezoelectric motor.

An aspect of some embodiments of the present invention relate toproviding an electric shaver in which the at least one piezoelectricmotor imparts rotary motion to the cutting blades via a geartransmission. In some embodiments of the present invention, the geartransmission is a planetary gear transmission.

The cutting blades are preferably mounted to at least one rotary, bladehead comprising a hub as described above. Each rotary blade head ispreferably coupled to a gear that is a planet gear of the planetarytransmission. The planet gears are preferably located inside and coupledto an annulus gear, which when rotated, rotates all the planetary gearsand thereby the rotary blade heads. The at least one piezoelectric motoris coupled to and rotates the annulus gear.

In some embodiments of the present invention, a planetary transmissioncomprises a sun gear that is coupled to each of the planet gears of therotary blade heads. In some planetary transmission configurationscomprising a sun gear, the annulus gear is absent and the sun gear iscoupled to at least one piezoelectric motor that turns the sun gear andthereby the planet gears. In some embodiments of the present inventionthe sun gear drives a rotary blade head.

An aspect of some embodiments of the present invention relates toproviding a shaver comprising at least one rotary blade head thatcomprises cutting blades having cutting edges located on a surface ofrevolution. The surface of revolution has an axis substantially parallelto an axis of rotation about which the rotary blade head is rotated. Theblade head is optionally coupled to a circularly cylindrical couplingsurface having an axis of rotation coincident with the axis of rotationof the blade head. At least one piezoelectric motor turns the couplingsurface and thereby the at least one rotary blade head.

An aspect of some embodiments of the present invention relate toproviding a shaver comprising at least one piezoelectric motor thatimparts oscillatory motion to cutting blades of the shaver. In someembodiments of the present invention the oscillatory motion isrotational. In some embodiments of the present invention the oscillatorymotion is linear. The cutting blades are mounted to or formed on, an atleast one “oscillatory blade head”

In some embodiments of the present invention, the at least oneoscillatory blade head comprises a first arc surface and a second arcsurface having a common axis of rotation. An arc surface is acylindrical surface having a directrix that is an arc of a circle, whicharc subtends less than 2π radians at the center of the circle. Cuttingblades are formed or mounted on the first arc surface so that theircutting edges are substantially parallel to the common axis of rotationor have directions that make small angles with the axis of rotation. Atleast one piezoelectric motor is coupled to the second arc surface,which is a coupling surface of the oscillatory blade head. The at leastone piezoelectric motor rotates the second arc surface, and thereby thefirst cylindrical surface and the cutting blades attached thereto, backand forth about the common axis of rotation.

In some embodiments of the present invention the shaver comprises anoscillatory blade head on which cutting blades are formed or mounted sothat their cutting edges are positioned in a linear array that defines alinear array axis of motion. The blade head comprises a planar couplingsurface. At least one piezoelectric motor is resiliently pressed to thecoupling surface so as to oscillate the coupling surface, and therebythe cutting blades, back and forth parallel to the axis of motion.

An aspect of some embodiments of the present invention relate toproviding a shaver in which oscillatory motion of cutting bladescomprised in the shaver is generated by exciting a resonant vibration ina blade head to which the cutting blades are attached.

The structure of the blade head, hereinafter referred to as a “resonantblade head”, and cutting blades is designed, using methods known in theart, so that the cutting blades have a resonant vibration mode at adesired resonant frequency. A force having a time dependent forcecomponent characterized by a frequency equal to or close to the resonantfrequency is applied to the resonant blade head. The force componentexcites the resonant vibration of the cutting blades to generate desiredmotion in the cutting blades. In some embodiments of the presentinvention the cutting blades are mounted to a resonant blade head in alinear array. In some embodiments of the present invention the cuttingblades are mounted to a blade head in a curved or circular array havingan axis of rotation.

In some embodiments of the present invention the force is generated by aconventional electric motor. In some embodiments of the presentinvention a piezoelectric motor generates the force. However, whilefrequencies of oscillation of cutting blades in a shaver are usually ina range from 50 Hz to 250 Hz, frequencies of resonant vibrations of mostpiezoelectric motors range from tens to hundreds of thousands of Hz. Inorder to use a “high frequency” piezoelectric motor to efficiently drivea “low frequency” resonant blade head, forces characterized by theresonant frequency of the blade head have to be generated from forcesprovided by the piezoelectric motor.

An aspect of some embodiments of the present invention relates toproviding a method for applying a force of appropriate frequency to aresonant blade head using a piezoelectric motor having a resonantfrequency higher than the resonant frequency of the blade head. Inaccordance with an embodiment of the present invention, forces providedby the piezoelectric motor are modulated by a time dependent modulationfunction having a frequency equal to or near to the resonant frequencyof the blade head. The modulation results in generating a time dependentforce characterized by the resonant frequency of the blade head. In someembodiments of the present invention the modulation function is anharmonic function. In some embodiments of the present invention, thetime dependent modulation function is generated by turning thepiezoelectric motor on and off at a frequency equal to or near to theresonant frequency of the blade head.

An aspect of some embodiments of the present invention relates toproviding a wet shaver that provides an improved shave, which issmoother than shaves provided by prior art wet shavers. Wet shavers areshavers comprising at least one razor blade having a cutting edge thatis drawn by hand over a region of skin generally moistened with waterand lathered with a lubricant, such as shaving cream, to remove hairfrom the skin. In an embodiment of the present invention, a wet shavercomprises a piezoelectric motor that is coupled to the at least onerazor blade. The piezoelectric motor and circuits and wires that providepower to the piezoelectric motor are preferably waterproofed with anappropriate flexible coating of insulating material to prevent damage tothe motor and shaver from moisture and to protect a user of the shaverfrom electric shock. In some embodiments of the present invention, thepiezoelectric motor is mounted in a waterproof compartment. When the wetshaver is used, the piezoelectric motor generates high frequencyoscillations in the cutting edge of the at least one razor. Theoscillations move the cutting edge of the at least one razorperpendicular to itself back and forth along the direction in which thecutting edge is drawn over the skin. The oscillations cause the cuttingedge of the at least one razor to move over the skin more smoothly thando cutting edges of razors in prior art wet shavers.

An aspect of an embodiment of the present invention relates to providinga “wet electric shaver” that is useable in the same manner thatconventional electric shavers are used and that is also useable withwater and shaving cream in the way that conventional wet shavers areused.

In embodiments of the present invention, such as for example any of theembodiments described above, the piezoelectric motor and its accessorycomponents are waterproofed with an appropriate flexible sealant. Theshaver can therefore be used as a “dry” electric shaver in theconventional manner or as a “wet” electric shaver with skin being shavedlubricated with water and/or a shaving cream. It should be noted thatunlike conventional electric motors, piezoelectric motors, such as thosedescribed in U.S. Pat. No. 5,616,980 or PCT Application PCT/IL99/00288and variants thereof, because of their relatively simple constructionand small number of moving parts, are relatively easily waterproofedwith a coating of a flexible insulating material. Such flexibleinsulating materials are well known in the art and suitable flexibleinsulating materials, for example Teflon and latex, which bond well tomaterial of the piezoelectric motor are readily available. It shouldfurther be noted that materials suitable for forming friction nubs thatefficiently transmit motion to a moveable body to which they are pressedwhen wet are available. Among these materials are, for example, Aluminaand titanium.

An aspect of some embodiments of the present invention relates toproviding a shaver in which a single piezoelectric motor drives aplurality of shafts to which rotary blade heads are coupled.

The piezoelectric motor, hereinafter referred to as a “star motor”,comprises a plurality of arms, hereafter referred to as “driving arms”that extend outwardly along radial directions, “starfish like” from acommon center. In some embodiments of the present invention, the motorcomprises a planar layer of piezoelectric material bonded to a layer ofnon-piezoelectric material, which is, optionally, a metal. At least oneelectrode is located on the layer of the piezoelectric material on aside of the piezoelectric material, which is not bonded to the metal. AnAC voltage difference applied between the at least one electrode and themetal layer generates longitudinal vibrations in each driving arm of thestar motor. Because, the metal layer does not expand with application ofan electric field to the metal, periodic expansion and contraction ofthe piezoelectric material in each driving arm caused by thelongitudinal vibrations generate mechanical forces that bend the arm andexcite a bending vibration mode of the arm. The combination oflongitudinal and bending vibration modes of the driving arm causes amotor coupling surface, optionally a friction nub, on the arm to executean elliptical vibration. The elliptical vibration of the motor couplingsurface of each driving arm is coupled to rotate a shaft mounted with arotary blade head. Star motors, in accordance with embodiments of thepresent invention may comprise different numbers of driving arms. Insome embodiments of the present invention, a star motor comprises, byway of example, two three or four driving arms that are used to drivetwo, three or four shafts.

In some star motors in accordance with an embodiment of the presentinvention the piezoelectric layer in driving arms of the motor that isexcited by an electric field is bonded to a piezoelectric layer ofmaterial to which an electric field is not applied. Mechanical stressbetween the excited piezoelectric layer and non-excited piezoelectriclayer generate bending motions in driving arms of the motor.

In some embodiments of the present invention, vibrations in driving armsof a star motor that are useful for transmitting motion to a moveableelement are not generated by mechanical forces between a layer ofmaterial in the driving arms. Instead, useful vibrations in the drivingarms are excited by electrifying appropriate configurations ofelectrodes on surface regions of the driving arms.

In some embodiments of the present invention bending vibrations indriving arms of star motors are generated by asymmetries in massdistributions of the driving arms. When longitudinal vibrations aregenerated in the driving arms forces accelerating the asymmetric massdistribution generate torque that excites bending vibrations in thedriving arms.

There is therefore provided in accordance with an embodiment of thepresent invention

A piezoelectric motor comprising: a layer of piezoelectric materialhaving narrow edge surfaces and first and second large face surfaces,formed with at least three arms, each extending radially outward from acommon central region and terminating in an end; at least one electrodeon the first face surface and at least one electrode on the second facesurface.

Optionally each arm has a bilateral axis of symmetry that extends fromthe central region. Optionally, each of the arms of the piezoelectriclayer is substantially rectangular. Optionally, each of the arms issubstantially trapezoidal with its width decreasing with distance fromthe central region.

In some embodiments of the present invention the thickness of eachpiezoelectric arm decreases with distance from the central region. Insome embodiments of the present invention junctions of an arm with thecentral region are curved.

In some embodiments of the present invention the piezoelectric motorcomprises a thin plate having two large face surfaces and at least threearms, said plate being substantially similar in shape to thepiezoelectric layer, wherein the first face surface of the piezoelectriclayer is aligned with and bonded to one of the face surfaces of theplate. Optionally, the thin plate is formed from a non-piezoelectricmaterial. Optionally, the material is non-conductive. Alternatively, thematerial is optionally a conductor.

In some embodiments of the present invention the at least one electrodeon the first face surface of the piezoelectric layer comprises a singlelarge electrode covering substantially the entire first surface.

In some embodiments of the present invention the at least one electrodeon the second face surface of the piezoelectric layer comprises a singlelarge electrode covering substantially the entire second surface.Optionally the piezoelectric motor comprises an AC voltage sourceconnected to the single electrode that electrifies the single electrodewith respect to the at least one electrode on the first surface, said atleast one electrode on the first surface being configured such that whenthe single electrode is electrified, mass points in the corners of theend of each arm execute elliptical vibratory motion perpendicular to theplane of the arm.

In some embodiments of the present invention the at least one electrodeon the second face surface comprises a single electrode on each arm thatcovers substantially all the area of the second surface on one side ofthe arm's axis of symmetry and substantially none of the area on theother side. Optionally, the single electrode on any one arm ishomologous with the single electrode on any of the other arms.Optionally, the electrodes on the second face surface are electricallyconnected.

In some embodiments of the present invention the at least one electrodeon the second face surface comprises first and second separateelectrodes on each arm that are located on opposite sides of the arm'sbilateral axis of symmetry and together cover substantially all the areaof the second surface in the region of the arm. Optionally, the firstand second electrodes on any one arm are homologous respectively withthe first and second electrodes on any of the other arms and all thefirst electrodes are connected to form a first set of electrodes and allthe second electrodes are connected to form a second set of electrodes.Optionally, the piezoelectric motor comprises a source of voltageconnected to the first and second sets of electrodes which electrifiesthe first and second electrodes with respect to the at least oneelectrode on the first surface with first and second AC voltagesrespectively that are 180° out of phase and wherein, the at least oneelectrode on the first surface is configured so that when the first andsecond sets of electrodes are electrified, mass points near oppositecorners of the end of each arm execute same sense elliptical vibratorymotion as seen from a point on the bilateral axis of symmetry of thearm.

In some embodiments of the present invention the at least one electrodeon the second face surface of the piezoelectric layer comprises fourelectrodes on each arm that are arranged in a checkerboard pattern witheach electrode located in a different quadrant of the second surface inthe region of the arm. Optionally, diagonally opposite electrodes oneach arm are electrically connected to form a first and a second pair ofdiagonally connected electrodes on each arm and wherein first and secondpairs of diagonal electrodes on each arm are homologous respectivelywith the first and second diagonal pairs of electrodes on any of theother arms of the motor. Optionally, all the first diagonal pairs ofelectrodes are electrically connected to form a first set of diagonalelectrodes and all the second pairs of diagonal electrodes areelectrically connected to form a second set of diagonal electrodes.

In some embodiments of the present invention the piezoelectric motorcomprises an AC voltage source connected to the electrodes whichelectrifies the first set of diagonal electrodes with respect to the atleast one electrode on the first surface while the second set ofdiagonal electrodes is grounded or floating, and the at least oneelectrode on the first surface is configured so that when the AC voltagesource electrifies the first set of electrodes, mass points in oppositecorners of the end of each arm execute clockwise elliptical vibratorymotion perpendicular to the plane of the motor as seen from a point onthe bilateral axis of symmetry of the arm.

In some embodiments of the present invention the piezoelectric motorcomprises an AC voltage source connected to the electrodes whichelectrifies the second set of diagonal electrodes with respect to the atleast one electrode on the first surface while the first set of diagonalelectrodes is grounded or floating, and the at least one electrode onthe first surface is configured so that when the AC voltage sourceelectrifies the second set of electrodes, mass points in oppositecorners of the end of each arm execute counterclockwise ellipticalvibratory motion perpendicular to the plane of the motor as seen from apoint on the bilateral axis of symmetry of the arm.

In some embodiments of the present invention the piezoelectric motorcomprises a mass element affixed to each arm on the first surface at adistance from the central region and wherein when longitudinalvibrations are excited in the arm the mass generates a torque thatexcites bending vibrations in the arm.

In some embodiments of the present invention the piezoelectric motorcomprises an AC voltage source connected to the at least one electrodeon the first surface and the at least one electrode on the secondsurface that electrifies the at least one electrode on the secondsurface with respect to the at least one electrode on the second surfaceand wherein the electrodes are configured so that when they areelectrified by the voltage source, vibratory motion is excited in eachof the arms.

There is further provided in accordance with an embodiment of thepresent invention a piezoelectric motor comprising: a thin plate formedfrom two layers of piezoelectric material bonded together, said platehaving narrow edge surfaces and first and second large face surfaces,formed with at least three substantially rectangular arms, each having abilateral axis of symmetry and extending radially outward from a commoncentral region and terminating in an end; first and second electrodescovering substantially the entire area of the first and second surfacesrespectively; and a medial electrode located between the piezoelectriclayers having an area substantially equal to the area of the firstelectrode.

Optionally, the piezoelectric layers are mirror images of each other.Optionally, the piezoelectric motor comprises a source of AC voltageconnected to the first, second and medial electrodes that electrifiesthe first and second electrodes with respect to the medial electrodewith AC voltages having a same frequency and phase but differentamplitudes.

Optionally, the piezoelectric layers have different thicknesses.Optionally, the piezoelectric motor comprises a source of AC voltageconnected to the first, second and medial electrodes that electrifiesthe first and second electrodes with respect to the medial electrodewith a same AC voltage.

In some embodiments of the present invention, the piezoelectric motorcomprises a friction nub located on the edge surface of the end of eachpiezoelectric arm.

In some embodiments of the present invention, the piezoelectric motorcomprises a single friction nub located on the second surface of thepiezoelectric layer near a corner of the end of each piezoelectric arm.

In some embodiments of the present invention, the piezoelectric motorcomprising a thin plate comprises on the surface of the thin plate thatis not bonded to the piezoelectric layer a single friction nub locatednear a corner of the end of each arm of the plate.

In some embodiments of the present invention the piezoelectric motorcomprises an extension for each arm formed from a non-piezoelectricmaterial that is bonded to the end of the arm, which extension comprisesa single friction nub located on a surface of the extension that isparallel to the plane of the arm and displaced from the bilateral axisof symmetry.

In some embodiments of the present invention the piezoelectric motorcomprises two substantially identical friction nubs located on thesecond surface in opposite corners of the end of each piezoelectric armand wherein a straight line connecting the friction nubs issubstantially perpendicular to the bilateral axis of symmetry of thearm.

In some embodiments of the present invention the piezoelectric motorcomprises, on the surface of the plate not bonded to the piezoelectriclayer, two substantially identical friction nubs located near corners ofthe end of each arm of the plate and wherein a straight line connectingthe friction nubs is substantially perpendicular to the bilateral axisof symmetry of the arm.

In some embodiments of the present invention, the piezoelectric motorcomprises an extension for each arm formed from a non-piezoelectricmaterial that is bonded to the end of the arm, which extension comprisesa friction nub on each side of the bilateral axis of symmetry of the armand wherein a straight line connecting the friction nubs issubstantially perpendicular to the bilateral axis of symmetry.

In some embodiments of the present invention, the piezoelectric motorcomprises a disk, having an axis of rotation perpendicular to surfacesthereof, mounted to the single friction nub of each arm, wherein theaxis of rotation is perpendicular to the plane of the arm and thefriction nub contacts a disk surface at a point on the disc surface forwhich a line from the point perpendicular to the axis of rotation issubstantially perpendicular to the bilateral axis of the arm. Optionallythe axis of rotation intersects the bilateral axis of symmetry of thearm.

In some embodiments of the present invention, the piezoelectric motorcomprises a disk, having an axis of rotation perpendicular to surfacesthereof for each arm, wherein a surface of the disc is resilientlypressed to both friction nubs of the arm and the disc's axis of rotationis perpendicular to and passes through the arm's bilateral axis ofsymmetry and a the line connecting the friction nubs.

In some embodiments of the present invention, the piezoelectric motorhas a rotational symmetry of order equal to the number of arms in themotor.

There is further provided, in accordance with an embodiment of thepresent invention, a piezoelectric motor comprising: a rectangular layerof piezoelectric material having short and long edges, a long axis ofsymmetry and first and second large face surfaces, at least oneelectrode on the first face surface and at least one electrode on thesecond face surface; a friction nub located near each corner of thepiezoelectric layer adjacent to at least one same short edge of thelayer wherein a straight line connecting the friction nubs issubstantially perpendicular to the long axis of symmetry; and an ACvoltage source connected to the electrodes that electrifies the at leastone electrode on the first face surface with respect to the at least oneelectrode on the second face surface, said electrodes having aconfiguration such that when electrified, the friction nubs execute samesense elliptical vibratory motion as seen from a point on the long axisof symmetry.

Optionally, the piezoelectric motor comprises a disk, having an axis ofrotation perpendicular to surfaces thereof, for each pair of frictionnubs near a same short edge, wherein a surface of the disc isresiliently pressed to both friction nubs of the pair of friction andthe disc's axis of rotation is perpendicular to and passes through thelong axis of symmetry and a line connecting the friction nubs.

There is further provided, in accordance with an embodiment of thepresent invention, a compound piezoelectric motor comprising: first andsecond mirror image piezoelectric motors according to any of claims33–40 having the axes of symmetry of their respective arms parallel andfriction nubs facing each other; a disk, having an axis of rotationperpendicular to surfaces thereof positioned between each arm of thefirst piezoelectric motor and its mirror image arm in the secondpiezoelectric motor, wherein the disc's axis of rotation isperpendicular to the bilateral axes of symmetry of the mirror image armsand each of the friction nubs of the arms is in contact with one of thedisk surfaces; and at least one elastic element that resiliently pressesthe first and second piezoelectric motors towards each other so thateach of the friction nubs of the motors is resiliently pressed to thedisc surface that it contacts.

There is further provided, in accordance with an embodiment of thepresent invention, a compound piezoelectric motor comprising: first andsecond mirror image piezoelectric motors according to claim 43 havingtheir respective long axes of symmetry parallel and friction nubs facingeach other; a disk, having an axis of rotation perpendicular to surfacesthereof which is positioned between each pair of friction nubs along ashort edge of the first motor and the mirror image pair of friction nubsof the second motor, wherein the disk's axis of rotation isperpendicular to the long axes of symmetry of the mirror image motorsand each of the friction nubs of the motors is in contact with one ofthe disk surfaces; and at least one elastic element that resilientlypresses the first and second piezoelectric motors towards each other sothat each of the friction nubs of the motors is resiliently pressed tothe disk surface that it contacts.

In some embodiments of the present invention, each disc surface isformed with a thin circular ridge having a center located on the axis ofrevolution of the disk and wherein each of the friction nubs of thepiezoelectric motor that contacts the surface contacts the ridge.

In some embodiments of the present invention, the discs are formed asgears and the motor comprises a gear mounted to the central region ofthe motor which meshes with all the discs.

In some embodiments of the present invention, each of the discs isformed with an edge surface and the motor comprises an additional dischaving an edge surface which is mounted to the central region of themotor so that the edge surface of the additional disc is in frictionalcontact with the edge surface of each of the other discs.

In some embodiments of the present invention, each disk is mounted witha shaft having an axis of rotation coincident with the disc's axis ofrotation.

In some embodiments of the present invention, the discs are mountedintegrally to the body of the motor.

There is further provided, in accordance with an embodiment of thepresent invention, a shaver comprising a motor according to claim 51wherein each shaft is mounted with a blade head having an axis ofrotation coincident with the axis of the shaft and at least one cuttingblade having a cutting edge for cutting hair that extends substantiallyradially away from the blade head's axis of rotation.

There is further provided in accordance with an embodiment of thepresent invention a shaver for cutting facial and body hair comprising:at least one blade head comprising at least one cutting blade having acutting edge for cutting hair; a coupling surface coupled to the atleast one blade head so that when the coupling surface moves, the bladehead moves; at least one piezoelectric motor having a motor-couplingsurface region resiliently pressed to the coupling surface; and adriving circuit that energizes the at least one piezoelectric motor andexcites thereby vibrations in the motor-coupling surface of thepiezoelectric motor that moves the coupling surface and thereby theblade head and at least one cutting blade.

In some embodiments of the present invention, the at least one bladehead has an axis of rotation about which the blade head is rotatable anda hub having a center through which the axis of rotation passes, towhich hub the at least one cutting blade is attached. Optionally, thecutting edge of each at least one cutting blade extends outward from theaxis of rotation in a general radial direction and wherein a portion ofthe cutting edge of each cutting blade lies close to or in a same planeperpendicular to the axis of rotation.

Additionally or alternatively, the blade head is rigidly attached to ashaft having an axis of rotation coincident with the axis of rotation ofthe hub.

In some embodiments of the present invention the coupling surface is asurface region of a disc mounted to the shaft, which surface region issubstantially perpendicular to the axis of rotation of the shaft.

In some embodiments of the present invention, the coupling surface is acircularly cylindrical coupling surface rigidly attached to the shaftand having an axis of rotation coincident with the axis of rotation ofthe shaft. Optionally, the coupling surface is a surface of the shaft.Alternatively, the coupling surface is a surface of a rim of a wheelrigidly mounted to the shaft.

In some embodiments of the present invention the at least one blade headcomprises two blade heads having parallel axes of rotation wherein: theat least one piezoelectric motor is located between the shafts of theblade heads so that a different motor-coupling surface of the at leastone piezoelectric motor contacts the coupling surface of each of theshafts; and including apparatus for generating at least one resilientforce that presses the coupling surfaces of the shafts to themotor-coupling surfaces of the at least one piezoelectric motor.

In some embodiments of the present invention the at least one blade headcomprises at least three blade heads having parallel axes of rotationthat intersect a common plane perpendicular to the axes at points thatare vertices of an equilateral polygon and comprising: at least onepiezoelectric motor located between each pair of adjacent shafts so thata different motor-coupling surface of the at least one piezoelectricmotor contacts the coupling surface of each of the shafts between whichthe at least one piezoelectric motor is positioned; and apparatus forapplying at least one resilient force so that all coupling surfaces ofthe shafts are resiliently pressed to motor-coupling surfaces ofpiezoelectric motors that they contact.

Preferably, all coupling surfaces are pressed to each of themotor-coupling surfaces of piezoelectric motors that they contact with asubstantially same magnitude force. Alternatively or additionally thepolygon is convex.

In some embodiments of the present invention the apparatus for applyinga resilient force comprises: a bearing surface associated with eachshaft; and an elastic element coupling each bearing surface to anadjacent bearing surface associated with each of two shafts adjacent tothe shaft with which the bearing surface is associated, which elasticelement operates on the bearing surface to produce a same magnitudeforce in directions from the bearing surface to each of the adjacentbearing surfaces. Preferably, the bearing surface associated with eachshaft is rotatable about the shaft.

Additionally or alternatively each bearing surface comprises a groovededge surface perpendicular to the axis of rotation of the shaft withwhich the bearing surface is associated. In some embodiments of thepresent invention the elastic element is a spring. In some embodimentsof the present invention the elastic element comprises a stretchedelastic band that passes through each groove.

Additionally or alternatively when each of the at least onepiezoelectric motor located between a pair of blade heads is energizedeach rotates the coupling surfaces of the blade heads it contacts with anon-oscillatory rotary motion in either a same clockwise orcounterclockwise direction.

In some embodiments of the present invention the at least one blade headhas an axis of rotation about which the at least one blade head isrotatable and the cutting edge of each of the at least one cutting bladelies substantially on cylindrical surface that has an axis of rotationcoincident with the axis of rotation of the blade head. Optionally, theat least one cutting blade comprises a plurality of cutting bladeshaving cutting edges that lie substantially on a same cylindricalsurface.

Alternatively or additionally, the coupling surface is a cylindricalsurface rigidly attached to the at least one cutting blade, having anaxis of rotation coincident with the axis of rotation of the blade head.

In some embodiments of the present invention, the directrices of thecylindrical coupling surface and the cylindrical surface on which thecutting edge of each of the at least one cutting blade lie are a samecircle or concentric circles. Preferably, the at least one piezoelectricmotor, when energized, rotates the coupling surface and thereby the atleast one cutting blade with a non-oscillatory rotary motion about theaxis of rotation.

In some embodiments of the present invention, the directrices of thecylindrical coupling surface and the cylindrical surface on which thecutting edge of each of the at least one cutting blade lie are arcs ofthe same or concentric circles.

In some embodiments of the present invention, the at least onepiezoelectric motor when energized oscillates the coupling surface andthereby the at least one cutting blade with a rotary motion about theaxis of rotation. In some embodiments of the present invention, the atleast one cutting blade has a resonant vibration mode and theoscillatory motion that the at least one piezoelectric motor transmitsto the coupling surface excites the resonant vibration mode.

In some embodiments of the present invention the coupling surface is aplanar surface rigidly attached to the blade head. Preferably, the atleast one piezoelectric motor oscillates the coupling surface, andthereby the blade head and at least one cutting blade, back and forthalong a single direction. Optionally, the at least one cutting bladecomprises a plurality of cutting blades mounted to the blade head in alinear array defined by an array axis parallel to the direction alongwhich the at least one piezoelectric motor oscillates the couplingsurface. In some embodiments of the present invention, the at least onecutting blade has a resonant vibration mode and the oscillations of theblade head generated by the at least one piezoelectric motor excites theresonant vibration mode of the at least one cutting blade.

In some embodiments of the present invention the at least one cuttingblade has a resonant vibration mode. Optionally, the coupling surface isa planar surface rigidly attached to the blade head.

In some embodiments of the present invention, when the driving circuitenergizes the piezoelectric motor, the motor-coupling surface of thepiezoelectric motor that is pressed to the coupling surface vibratessubstantially only in a direction perpendicular to the coupling surface.As a result, the motor-coupling surface impacts the coupling surfaceintermittently and excits thereby the resonant vibration mode of the atleast one cutting blade.

In some embodiments of the present invention, the driving circuitenergizes the at least one piezoelectric motor with a time varyingvoltage characterized by a frequency higher than the resonant frequencyof the at least one cutting blade. The time varying voltage isoptionally an harmonically varying voltage. Alternatively oradditionally the driving circuit modulates the time varying voltage witha modulation function characterized by a frequency equal to or close tothe resonant frequency. In some embodiments of the present invention themodulation function is a cyclical hat function. In some embodiments ofthe present invention the modulating function is an harmonic function.

In some embodiments of the present invention the at least one cuttingblade comprises a plurality of cutting blades mounted to a surface in alinear array defined by an array axis. Preferably, the coupling surfaceis perpendicular to the array axis.

In some embodiments of the present invention the at least one cuttingblade comprises a plurality of cutting blades mounted to a common shafthaving an axis of rotation and the cutting edge of each cutting bladeextends away from the axis of rotation in a general radial direction.Preferably, the coupling surface is rigidly attached to the shaft and iscoplanar with the axis of rotation of the shaft.

In some embodiments of the present invention a first gear is mounted tothe shaft and a coupling surface is coupled to the first gear via asecond gear. Optionally, the at least one blade head comprises aplurality of blade heads. In some embodiments of the present invention,the first gear on the shaft of each blade head of the plurality of bladeheads is a planet gear of a planetary gear transmission. Preferably, theplanetary gear transmission comprises an annulus gear having an axis ofrotation and the planet gears mesh with the annulus gear and rotate whenthe annulus gear rotates. The coupling surface is, optionally, acircularly cylindrical coupling surface rigidly attached to the annulusgear and has an axis of rotation coincident with the axis of rotation ofthe annulus gear.

In some embodiments of the present invention the at least one blade headcomprises a plurality of blade heads and the axes of the respectiveshafts of the blade heads are parallel. In some embodiments of thepresent invention, the axes of rotation intersect a same circle.Alternatively or additionally, the at least one piezoelectric motor issituated between the center of the circle and each blade head.Preferably, the shaver comprises a resilient body located at the centerof the circle that presses on a surface region of the at least onepiezoelectric motor that lies between the center of the circle and eachof the plurality of blade heads and presses thereby the motor-couplingsurface of the at least one piezoelectric motor resiliently to thecoupling surface that it contacts.

There is further provided in accordance with an embodiment of thepresent invention a wet shaver for shaving hair on a region of skinlubricated with water comprising: a razor blade having a straightcutting edge that is designed to be drawn over the region of skin in adirection perpendicular to the straight edge to shave the skin; acoupling surface coupled to the razor blade such that when the couplingsurface moves, the razor blade moves; at least one piezoelectric motorhaving a motor-coupling surface resiliently pressed to the couplingsurface; and a driving circuit that energizes the at least onepiezoelectric motor and excites thereby vibrations in the motor-couplingsurface of the piezoelectric motor that moves the coupling surface andthereby the razor blade head and cutting edge.

In some embodiments of the present invention vibrations in themotor-coupling surface of the piezoelectric motor generate oscillatoryrotary motion of the razor blade about an axis of rotation parallel tothe cutting edge. In some embodiments of the present invention, the wetshaver comprises a mounting plate to which the razor blade is mountedand wherein the coupling surface is a surface of the mounting plate.Preferably, the mounting plate is attached to a handle by a hinge havingan axis of rotation parallel to the cutting edge and the razor bladerotates about the axis of rotation. Preferably, the motor-couplingsurface of the piezoelectric motor that presses against the couplingsurface vibrates substantially only in directions perpendicular to thecoupling surface when the driving circuit energizes the piezoelectricmotor.

In some embodiments of the present invention the motor-coupling surfaceof the at least one piezoelectric motor is a surface region of a tip ofa conical nub bonded to a surface of the piezoelectric motor.

In some embodiments of the present invention vibrations in themotor-coupling surface of the piezoelectric motor generate oscillatorylinear motion of the razor blade and thereby the cutting edge, back andforth parallel to the cutting edge. Optionally, the coupling surface isa planar surface parallel to the cutting edge that is rigidly attachedto the razor blade. Preferably, the vibrations in the motor-couplingsurface of the at least one piezoelectric motor are alternatingclockwise and counterclockwise elliptical vibrations.

In some embodiments of the present invention, the motor-coupling surfaceof the at least one piezoelectric motor is a surface region of afriction nub bonded to a surface of the piezoelectric motor.

In some embodiments of the present invention, the piezoelectric motorvibrates the cutting edge of the razor blade with a frequency greaterthan 5,000 Hz. In some embodiments of the present invention, thepiezoelectric motor vibrates the cutting edge of the razor blade with afrequency greater than 10,000 Hz. In some embodiments of the presentinvention, the piezoelectric motor vibrates the cutting edge of therazor blade with a frequency greater than 20,000 Hz.

In some embodiments of the present invention, the at least onepiezoelectric motor is waterproofed with a coating of a flexibleinsulating material.

There is further provided in accordance with an embodiment of thepresent invention a piezoelectric motor comprising: a piezoelectricvibrator having electrodes connected to conducting leads; and a flexibleinsulating coating that covers the vibrator, the electrodes and theleads.

In some embodiments of the present invention the piezoelectric motorcomprises a nub mounted on a surface of the vibrator that is pressed toa body that the motor moves. Optionally, the nub is a replaceable nubmountable to the vibrator after the vibrator is covered with theinsulating coating.

In some embodiments of the present invention the insulating coating is acoating of Teflon. In some embodiments of the present invention thecoating is a coating of latex.

There is further provided, in accordance with an embodiment of thepresent invention, a piezoelectric motor for transmitting motion to abody in only one direction comprising: a relatively thin rectangularpiezoelectric vibrator formed from at least one thin rectangular layerof piezoelectric material having first and second relatively largeplanar face surfaces and short and long narrow edge surfaces; a firstelectrode covering areas of three quadrants of a first face surface andsubstantially no area of a fourth quadrant of the face surface of atleast one piezoelectric layer of the at least one piezoelectric layer,and a second electrode on the second face surface of the at least onepiezoelectric layer having the first electrode, the second electrodehaving a surface region opposite the first electrode.

In some embodiments of the present invention, the piezoelectric motorcomprises a third electrode covering an area of the fourth quadrant ofthe first face surface. In some embodiments of the present invention,the first electrode covers substantially all the three quadrants. Insome embodiments of the present invention, the first electrode is Lshaped. In some embodiments of the present invention, the thirdelectrode covers substantially all of the area of the fourth quadrant.In some embodiments of the present invention, the at least one layercomprises a plurality of layers stacked with the long edges of alllayers parallel.

There is further provided, in accordance with an embodiment of thepresent invention a piezoelectric motor comprising: a piezoelectricvibrator having an axis of symmetry and a first vibration mode, whichwhen excited generates oscillatory motion of mass points in the vibratorparallel to the axis of symmetry; and at least one friction nub having acenter of mass displaced from the axis of symmetry, as a result of whichdisplacement, when the vibration mode is excited, torque is generated onthe vibrator that excites a second vibration mode of the vibrator.

In some embodiments of the present invention, the friction nub islocated on a narrow edge surface of the piezoelectric motor.Additionally or alternatively, the first and second vibration modescombine to move the friction nub with an elliptical vibratory motion.

In some embodiments of the present invention, the piezoelectric vibratorcomprises a relatively thin rectangular plate of piezoelectric materialhaving first and second relatively large planar face surfaces and shortand long narrow edge surfaces and the axis of symmetry is a line thatpasses through the center of the vibrator parallel to the long edges ofthe vibrator. In some embodiments of the present invention, therectangular plate is formed from a plurality of layers of materialcomprising at least one layer of piezoelectric material.

Alternatively or additionally, the friction nub consists of a firstportion having a center of mass that lies on the axis of symmetry whichfirst portion is connected to a second portion having a center of massdisplaced from the axis of symmetry. In some embodiments of the presentinvention, the friction nub is formed in the shape of an L and the firstand second portions are first and second legs of the L. Preferably, thefirst and second legs are orthogonal. Preferably, the friction nub issituated on a short edge surface of the vibrator and the axis ofsymmetry passes through the center of mass of the first leg.

Preferably, the second leg extends in a direction that is substantiallyperpendicular to the planes of the face surfaces of the vibrator.Alternatively, the second leg extends in a direction that issubstantially parallel to the planes of the face surfaces of thevibrator.

In some embodiments of the present invention, the piezoelectric motorcomprises two friction nubs located on opposite short edge surfaces ofthe vibrator and the centers of mass of the two friction nubs arecoplanar and displaced from the axis of symmetry in opposite directionsby a same distance.

There is further provided in accordance with an embodiment of thepresent invention a piezoelectric motor comprising: a vibrator having avibration mode, which vibration mode, when excited, generatesoscillatory motion of mass points in the vibrator parallel to a firstdirection; and a friction nub for which vibrations of mass points of thevibrator parallel to the first direction generate an oscillatory forcehaving an action line that does not intersect the center of mass of thefriction nub which force generates torque on the body of the nub thatexcites a bending vibration mode of the friction nub.

In some embodiments of the present invention, the friction nub consistsof a first portion having a center of mass through which the action linepasses, which first portion is connected to a second portion having acenter of mass displaced from the action line. Optionally, the frictionnub is formed in the shape of an L and wherein the first and secondportions are first and second legs of the L. Preferably the first andsecond legs are orthogonal.

In some embodiments of the present invention, the piezoelectric vibratorcomprises a relatively thin rectangular plate of piezoelectric materialhaving relatively large planar face surfaces, long edge surfaces andfirst and second short edge surfaces and the first direction is parallelto the long edges of the vibrator.

In some embodiments of the present invention, the friction nub issituated on a first short edge surface of the vibrator and the line ofaction passes through the center of mass of the first leg. Preferably,the second leg extends in a direction that is substantiallyperpendicular to the planes of the face surfaces of the vibrator.Preferably, the first leg extends in a direction that is substantiallyparallel to the planes of the face surfaces of the vibrator.

In some embodiments of the present invention, the piezoelectric vibratorcomprises a second friction nub located on the second short edge surfaceof the vibrator and the second legs of the first and second frictionnubs point in opposite directions with respect to the face surfaces ofthe vibrator.

There is further provided in accordance with an embodiment of thepresent invention, a piezoelectric motor comprising: a relatively thinrectangular piezoelectric vibrator formed from at least one thinrectangular layer of piezoelectric material having first and secondrelatively large planar face surfaces and short and long narrow edgesurfaces; four electrodes on a first face surface of a piezoelectriclayer of the at least one piezoelectric layer, each of which is locatedin a different quadrant of the first face surface of the layer; anelectrode on the second face surface of the piezoelectric layer having asurface region opposite each of the electrodes on the first facesurface; and a driving circuit that electrifies each electrode of twodifferent first and second sets of three of the four electrodes on thefirst face surface with a same voltage to generate respectivelyclockwise and counterclockwise elliptical motion of mass points of thevibrator.

Preferably, each of the electrodes on the first face surface coverssubstantially all of the area of the quadrant in which it is located.Alternatively, or additionally the at least one layer comprises aplurality of layers.

There is further provided in accordance with an embodiment of thepresent invention a method for rotating a plurality of shafts havingaxes of rotation comprising: positioning the shafts with their axes ofrotation parallel so that the axes intersect a common planeperpendicular to the shafts at points that are vertices of a polygon;providing each shaft with a circularly cylindrical coupling surfacehaving an axis of rotation coincident with the axis of rotation of theshaft; positioning at least one piezoelectric motor between each pair ofshafts that have axes at adjacent vertices of the polygon so that adifferent motor-coupling surface of the at least one piezoelectric motorcontacts a coupling surface of each of the shafts between which the atleast one piezoelectric motor is positioned; urging the axis of rotationof each shaft with a resilient force so that all coupling surfaces ofthe shafts are resiliently pressed to each of the motor-couplingsurfaces of piezoelectric motors that they contact with a substantiallysame magnitude force; and energizing the piezoelectric motors so thattheir respective motor-coupling surfaces that contact coupling surfacesof the shafts vibrate and rotate thereby the shafts.

In some embodiments of the present invention, the polygon isequilateral. Additionally or alternatively, the polygon is convex.

In some embodiments of the present invention, urging the axis ofrotation of each shaft with a resilient force comprises: mounting abearing to each shaft, which bearing is rotatable about the shaft; andconnecting each bearing to each of two adjacent bearings with an elasticelement that operates on the bearing with a same magnitude force indirections from the bearing to each adjacent bearing along a directionparallel to the side of the polygon between the bearing and the adjacentbearing. In some embodiments of the present invention, each bearingcomprises a grooved edge perpendicular to the axis of rotation of theshaft on which the bearing is mounted. Preferably, connecting eachbearing comprises looping a same stretched elastic element through allthe grooves.

In some embodiments of the present invention, urging the axis ofrotation of each shaft with a resilient force comprises: forming agroove in a circularly cylindrical surface rigidly attached to eachshaft, which cylindrical surface has an axis of rotation coincident withthe axis of rotation of the shaft; and looping a same stretched elasticelement through all the grooves.

There is further provided, in accordance with an embodiment of thepresent invention, a method for moving a body comprising: forming thebody so that it has a resonant vibration mode characterized by aresonant frequency; coupling a piezoelectric motor to the body; andenergizing the piezoelectric motor with a time varying voltage having afrequency component equal to or near to the resonant frequency ofvibration of the body and transmitting thereby energy into the resonantvibration mode of the body.

In some embodiments of the present invention, energizing thepiezoelectric motor comprises energizing the piezoelectric motor with atime varying voltage characterized by a frequency higher than theresonant frequency of the body and modulating the time varying voltagewith a modulation function characterized by a frequency equal to orclose to the resonant frequency. Optionally, the modulation function isa cyclical hat function. Alternatively the modulating function is,optionally, an harmonic function. Alternatively or additionally, thetime varying voltage is an harmonically varying voltage.

There is further provided, in accordance with an embodiment of thepresent invention, a method of moving a body comprising: resilientlypressing a friction nub of a vibrator of a piezoelectric motor to thebody, which vibrator has an axis of symmetry and wherein the frictionnub has a center of mass displaced from the axis of symmetry; andenergizing the piezoelectric motor to excite a vibration mode thatgenerates oscillatory motion of mass points in the vibrator parallel tothe axis of symmetry.

There is further provided, in accordance with an embodiment of thepresent invention, a method of moving a body comprising: resilientlypressing a friction nub of a vibrator of a piezoelectric motor having avibration mode that generates torque in the friction nub; and energizingthe piezoelectric motor to excite the vibration mode that generates thetorque in the friction nub.

BRIEF DESCRIPTION OF FIGURES

The invention will be more clearly understood from the followingdescription of embodiments thereof read with reference to the figuresthat are attached hereto. In the figures, identical structures, elementsor parts that appear in more than one figure are generally labeled withthe same numeral in all the figures in which they appear. Dimensions ofcomponents and features shown in the figures are chosen for convenienceand clarity of presentation and are not necessarily shown to scale. Thefigures are listed below.

FIGS. 1A–1D schematically show a rotary blade head of a shaver coupledto at least one piezoelectric motor, in accordance with an embodiment ofthe present invention;

FIG. 1E schematically shows a partial cutaway view of a shavercomprising two rotary blade heads of a type shown in FIGS. 1A–1C, inaccordance with an embodiment of the present invention;

FIGS. 2A–2E schematically show various configurations of multiple rotaryblade heads coupled to piezoelectric motors, in accordance withembodiments of the present invention;

FIG. 2F schematically shows a piezoelectric motor useable to rotaterotary blade heads in configurations shown in FIGS. 2A–2E, in accordancewith embodiments of the present invention;

FIGS. 3A and 3B schematically show various configurations of threerotary blade heads coupled to piezoelectric motors, in accordance withembodiments of the present invention;

FIG. 4 schematically shows a partial cut-away illustration of threerotary blade heads coupled to a piezoelectric motor via a planetary geartransmission, in accordance with an embodiment of the present invention;

FIG. 5 schematically shows a rotary blade head, in which cutting bladesare parallel to an axis of rotation of the blade head, coupled to apiezoelectric motor, in accordance with an embodiment of the presentinvention;

FIGS. 6A and 6B schematically show an oscillatory blade head and avariation thereof respectively, coupled to a piezoelectric motor, inaccordance with an embodiment of the present invention;

FIG. 7 schematically shows another oscillatory blade head coupled to apiezoelectric motor, in accordance with an embodiment of the presentinvention;

FIG. 8 schematically shows a resonant blade head coupled to apiezoelectric motor, in accordance with an embodiment of the presentinvention;

FIG. 9 schematically shows another resonant blade head coupled to apiezoelectric motor, in accordance with an embodiment of the presentinvention;

FIG. 10 schematically shows a wet shaver, in accordance with anembodiment of the present invention;

FIG. 11A schematically shows a star piezoelectric motor having threedriving arms, in accordance with an embodiment of the present invention;

FIG. 11B schematically shows another star piezoelectric motor havingthree driving arms, in accordance with an embodiment of the presentinvention;

FIG. 11C schematically shows the star motor shown in FIG. 11A rotatingthree shaver rotary blade heads, in accordance with an embodiment of thepresent invention;

FIG. 12A schematically shows two star motors of a type shown in FIGS.11A and 11C driving three rotary blade heads, in accordance with anembodiment of the present invention;

FIG. 12B schematically shows apparatus that presses star motors shown inFIG. 12A resiliently towards coupling discs of shafts that the starmotors drive, in accordance with an embodiment of the present invention;

FIG. 12C schematically shows a side view of apparatus that presses starmotors shown in FIG. 12A resiliently towards coupling discs of shaftsthat the star motors drive, in accordance with an embodiment of thepresent invention;

FIG. 12D schematically shows a method and apparatus for mounting shaftsthat are rotated by the star motors shown in FIGS. 12A–12C to themotors, in accordance with an embodiment of the present invention;

FIG. 12E schematically shows star motors shown in FIGS. 12A–12C coupledto shafts via coupling discs formed with circular ridges for couplingfriction nubs of the motors to the coupling discs, in accordance with anembodiment of the present invention;

FIG. 13A schematically shows a variation of the star motor shown inFIGS. 11A–12A, in accordance with an embodiment of the presentinvention;

FIG. 13B schematically shows a star motor comprising two piezoelectriclayers, in accordance with an embodiment of the present invention;

FIG. 13C schematically shows a star motor in which an asymmetrical massdistribution is used to excite bending vibrations in driving arms of themotor, in accordance with an embodiment of the present invention;

FIG. 14A schematically shows another star piezoelectric motor havingthree driving arms, in accordance with an embodiment of the presentinvention;

FIG. 14B schematically shows the star motor shown in FIG. 14A rotatingthree rotary blade heads, in accordance with an embodiment of thepresent invention;

FIG. 14C schematically shows another star motor, which is similar to thestar motor shown in FIGS. 14A and 14B, in accordance with an embodimentof the present invention;

FIGS. 15A and 15B schematically show star motors having two and fourdriving arms respectively, in accordance with embodiments of the presentinvention;

FIG. 16 schematically shows a star motor comprising three driving armsrotating four rotary blade heads, in accordance with an embodiment ofthe present invention; and

FIG. 17 schematically shows another star motor, in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1A schematically shows a piezoelectric motor 20 coupled to a rotaryblade head 22 of a shaver. Rotary blade head 22 optionally comprises aplurality of cutting blades 24, having cutting edges 26, that areattached to a hub 28. Each of cutting edges 26 optionally extends from apoint at or near to hub 28 in a general radial direction away from hub28. Cutting edges 26 in FIG. 1A and figures that follow are shown asstraight and extending radially from hub 28 by way of example and forconvenience of presentation. Cutting edges 26, in accordance withembodiments of the present invention, may have shapes different fromthose shown and such different shapes can be advantageous. Cutting edges26 may be formed in any of many shapes known in the art and may, forexample, be straight and extend away from hub 28 in directions that areangled with respect to radial directions or they may be curved.

Rotary blade head 22 is mounted in the shaver so that cutting edges 26of cutting blades 24 are positioned close to a perforated foil (notshown) of the shaver. A shaft 30 preferably connects rotary blade 22 toa “coupling” wheel 32 having a circularly cylindrical surface 34 whichfunctions as a coupling surface for rotary blade head 22. Shaft 30,cylindrical surface 34 and rotary blade head 22 have a common axis ofrotation indicated by a dashed line 36.

Piezoelectric motor 20 is optionally of a type described in U.S. Pat.No. 5,616,980 or PCT Application PCT/IL99/00288, referenced above, orvariants thereof. By way of example, and for convenience ofpresentation, piezoelectric motor 20 in FIG. 1 and piezoelectric motorsshown in the other figures are similar to types of piezoelectric motorsshown in U.S. Pat. No. 5,616,980. Other piezoelectric motors known inthe art may be substituted for the types shown.

Piezoelectric motor 20 optionally comprises a thin rectangularpiezoelectric vibrator 40 having long edge surfaces 49, short edgesurfaces 50 and 51 and a top planar “face” surface 42 and a bottomplanar “face” surface 44. A long axis 53 of piezoelectric motor 20,shown as a dashed line, passes through the centers of short edgesurfaces 50 and 51 parallel to long edges 49 of the piezoelectric motor.Top surface 42 optionally comprises four quadrant electrodes 46 that arelocated in a symmetric checkerboard pattern on top face surface 42. Asingle large electrode, not shown, is located on bottom surface 44.Piezoelectric motor 20 optionally comprises a friction nub 48 on shortedge surface 50, preferably located at the center of the edge. Aresilient force represented by a block arrow 52 is applied topiezoelectric motor 20 using methods known in the art to press frictionnub 48 to coupling surface 34.

When the shaver is in use, an AC voltage difference from an appropriatedriving circuit (not shown) is preferably applied between the largeelectrode and two quadrant electrodes 46 that are diagonally oppositeeach other. In some embodiments of the present invention the other twoquadrant electrodes 46 may be either floating or grounded. Optionally,the driving circuit is similar to a type of driving circuit described inPCT Application PCT/IL99/00520, referenced above, and the diagonalelectrodes that are not electrified with respect to the large electrodeare either short circuited to the large electrode or connected to thelarge electrode via a capacitor. Electrifying electrodes 46 using themethods described in the PCT/IL99/00520 improves the efficiency andquality of operation of piezoelectric motor 20.

It should be noted that electrodes 46 may be electrified, in accordancewith embodiments of the present invention, in other than the “diagonal”electrification configurations described above or using other drivingcircuits. Furthermore, voltage differences applied between electrodes 46and the large electrode may, in accordance with embodiments of thepresent invention, have other than AC harmonic waveforms. For example,the waveforms may be pulsed triangular waveforms and/or unipolarwaveforms and three electrodes 46 may be electrified simultaneously togenerate appropriate vibrations in piezoelectric motor 20. Differentelectrode electrification configurations and voltage waveforms aredescribed in U.S. Pat. No. 5,616,980 referenced above.

The applied AC voltage excites longitudinal and transverse vibrationmodes in vibrator 40 that generate elliptical motion of friction nub 48,which elliptical motion rotates coupling surface 34 and thereby cuttingblades 24 rapidly about axis of rotation 36. The radius of couplingsurface 34 is determined so that, at a linear velocity at which frictionnub 48 moves relative to coupling surface 34, rotary blade head 22rotates with a desired angular velocity. The foil (not shown) of theshaver behind which cutting blades 24 are located is pressed to andmoved over a region of skin to be shaved. Hairs that poke throughperforations in the foil are cut off by the rapidly moving cuttingblades 24.

Quadrant electrodes 46 in the configuration shown in FIG. 1 can beelectrified using any of the electrification schemes noted above togenerate both clockwise and counter clockwise elliptical vibrations inpiezoelectric motor 20, which rotate coupling wheel 32 and cuttingblades 24 respectively counterclockwise and clockwise. In the case wherediagonal electrode pairs are used to generate the elliptical vibrations,the direction of the elliptical motion depends upon which two diagonallyopposite electrodes 34 are electrified. In general however, it issufficient and desirable for the purposes of shaving to rotate cuttingblades 24 in one direction only.

Therefore, in some embodiments of the present invention, piezoelectricmotor 20 has an electrode configuration that enables generatingelliptical motion in friction nub 48 in one direction only. Inset 54 inFIG. 1 shows a piezoelectric motor 56 similar to piezoelectric motor 20that has an electrode configuration that enables excitation ofelliptical motion in friction nub 48 in only one direction. Inpiezoelectric motor 56 top planar face surface 42 has a three-quarterelectrode 58 and a quadrant electrode 60 instead of four quadrantelectrodes 46. As in piezoelectric motor 20, piezoelectric motor 56 hasa large electrode (not shown) on bottom planar face surface 44. Whenoperating piezoelectric motor 56, an AC voltage is applied betweenthree-quarter electrode 58 and the large electrode. Quadrant electrode60 may be floating, grounded or connected to the large electrode.Voltage applied between three-quarter electrode 58 and the largeelectrode generates only counter clockwise elliptical vibrations infriction nub 48. Quadrant electrode 60 is used only during manufactureof piezoelectric motor 56 to set the polarization of piezoelectric motor56. A three-quarter electrode 58, in accordance with an embodiment ofthe present invention, can be formed on piezoelectric motor 56 withquadrant electrode 60 located in any one of the four quadrant positionsof a quadrant electrode 46 shown on piezoelectric motor 20. Whenelectrified, configurations of a three-quarter electrode 58 and aquadrant electrode 60 on a motor 56 that have their respective quadrantelectrodes located along a same edge of planar face surface 42, exciteelliptical vibrations in opposite directions.

In some embodiments of the present invention three-quarter electrode 58may cover less than three-quarters of planar face surface 44 and mayhave a shape different from the L shape of electrode 58 shown in inset54. Any electrode that covers substantially all of the area covered bythe area covered by the legs of L shaped electrode 58 will exciteelliptical vibrations in friction nub 48 in the same direction aselectrode 58. Preferably, the area of the electrode is substantiallylarger than the area of two quadrant electrodes 46. In some embodimentsof the present invention, electrode 58 is shaped to optimizecorrespondence between the shape of electrode 58 and an energydistribution of a vibration mode of the motor that electrode 58 is usedto excite.

It should be noted of course that three quadrant electrodes 46 ofpiezoelectric motor 20 can be electrically connected and electrified toexcite vibrations in piezoelectric motor 20 in the same way thatthree-quarter electrode 58 excites vibrations in piezoelectric motor 56.In some embodiments of the present invention three quadrant electrodesare connected by a switching circuit and different sets of threequadrant electrodes are electrified to generate clockwise andcounterclockwise elliptical vibrations. The advantage of using threequadrant electrodes or a three-quarter electrode having a size largerthan two quadrant electrodes to excite vibrations, is that the motor mayprovide more power for a same applied voltage than when only twoquadrant electrodes are used to excite the vibrations.

(The excitation of vibrations in a piezoelectric motor similar topiezoelectric motor 20 by electrifying more than two quadrant electrodesis known in the art and is described for example in U.S. Pat. No.5,616,980. However, in prior art electrification schemes in which morethan two quadrant electrodes are electrified, at least one of theelectrified quadrant electrodes is electrified with a voltage differentfrom the others.)

An electrode configuration comprising a three-quarter electrode 58 and aquadrant electrode 60 has been shown in FIG. 1A for a piezoelectricmotor comprising a vibrator formed as a single thin rectangular plate.Such an electrode configuration is also useable, in accordance withembodiments of the present invention, as an electrode configuration onat least one layer of a multilayer piezoelectric motor of a type, forexample, described in PCT Application PCT/IL99/00288. Furthermore,whereas the three-quarter electrode 58 and quadrant electrode 60configuration has been described with reference to piezoelectric motorsshown in FIGS. 1A and 1B, such an electrode configuration is useable ona piezoelectric motor in all embodiments of the present invention inwhich blade heads are rotated in one direction.

In some embodiments of the present invention at least one hole is formedin vibrator 40 of piezoelectric motor 20 or 56. The at least one holeoptimizes the amount by which excitation curves of longitudinal andtransverse vibration modes in vibrator 40 that are used to generateelliptical motion of friction nub 48 overlap. The optimized overlapimproves the efficiency of operation of piezoelectric motor.

Inset 54 schematically shows a piezoelectric motor 55 similar topiezoelectric motor 20 having holes 61 formed in vibrator 40 to improvethe efficiency of operation of the piezoelectric motor. Piezoelectricmotor 55 is assumed, by way of example, to operate by exciting a firstlongitudinal resonant vibration mode and a second transverse vibrationmode of vibrator 40. Holes 61 are located along axis 53 at antinodes ofthe second transverse vibration mode. Whereas holes 61 are shown formedin piezoelectric motor 55, which has a “four quadrant” electrodeconfiguration, holes 61 may of course be used with other electrodeconfigurations, such as that shown for motor 56, that are used tosimultaneously excite longitudinal and transverse vibration modes in apiezoelectric vibrator.

FIG. 1B schematically shows an alternate method of coupling at least onepiezoelectric motor 20 to rotary blade head 22, in accordance with anembodiment of the present invention. In FIG. 1B a shaft 30 connectsrotary blade head 22 to a “coupling” disc 64. A resilient forcerepresented by block arrow 52 urges piezoelectric motor 20 in adirection so that friction nub 48 presses against a region of a bottomsurface 66 of coupling disc 64. Vibrations of friction nub 48 exert atorque on coupling disc 64 that rotates the disc and rotary blade head22. Whereas FIG. 1B shows a piezoelectric motor 20 coupled to couplingdisc 64, any of the piezoelectric motors shown in FIG. 1A or appropriatevariations thereof (such as multilayer piezoelectric motors described inPCT Application PCT/IL99/00288), or other motors known in the art may besimilarly coupled to coupling disc 64.

FIG. 1C schematically shows blade head 22 coupled to two piezoelectricmotors 41 in accordance with an embodiment of the present invention.Each of piezoelectric motor 41 comprises a thin rectangular vibrator 40having large planar face surfaces 42 and a long axis 53 shown with adashed line. A friction nub 43 is, optionally, mounted to a short edge50 of the piezoelectric vibrator so that the center of mass of thefriction nub is offset from axis 53. Preferably, friction nub 43 issituated at the center of short edge 50 and the offset of its center ofmass is caused by an asymmetric shape of friction nub 43 with respect toaxis 53. In FIG. 1C friction nub 43 is L shaped and comprises a stem 45that extends parallel to axis 53 and a head 47 that extends to one sideof axis 53, preferably at right angles to axis 53. Head 47 generates anasymmetry in friction nub 43 with respect to axis 53 that shifts thecenter of mass of friction nub 43 away from axis 53 in a directionperpendicular to the planes of face surfaces 42 of vibrator 40. Aresilient force 52 operates on piezoelectric motor 41 to press frictionnub 43 to coupling surface 34 of coupling wheel 32.

Preferably a single large electrode 39 is located on each planar facesurface 42 of piezoelectric vibrator 41. When electrodes 39 areelectrified by an appropriate AC voltage, a resonant longitudinalvibration mode is excited in vibrator 40 that moves friction nub 43 backand forth parallel to axis 53. Because the center of mass of frictionnub 43 is displaced from axis 53, accelerations caused by thereciprocating motion generate torque on friction nub 43. The torqueexcites a bending vibration mode in friction nub 43 that moves frictionnub 43 back and forth in directions indicated by double arrowhead line78 perpendicular to the planes of face surfaces 42. Preferably, thebending vibration mode of friction nub 43 has a frequency close to thefrequency of the longitudinal vibration mode excited by the AC voltage.The longitudinal motion along axis 53 and the back and forth vibrationexcited by the asymmetry of friction nub 43 combine to cause a motorcoupling surface of friction nub 43 to vibrate with an elliptical motionthat rotates coupling wheel 32 and blade head 22.

Elliptical motion of a (symmetrical) friction nub on edge 50 can also beexcited by positioning the friction nub on edge 50 so that its center ofmass is displaced from axis 53. The displacement generates a torque onvibrator 40 that excites a transverse vibration mode in vibrator 40perpendicular to axis 53. The longitudinal motion along axis 53 and thetransverse vibration mode combine to cause the friction nub to vibratewith an elliptical motion parallel to the planes of face surfaces 42.The elliptical motion can be used to rotate coupling wheel 32 ifpiezoelectric motor 41 is rotated 90° about axis 53. Energy coupling toa particular direction of an elliptical motion of the friction nub mayalso be induced and/or enhanced by mitering a corner of the vibrator.

Piezoelectric motor 41 operates most efficiently when electrification oflarge electrodes 39 excites only a single desired longitudinal resonantvibration of piezoelectric vibrator 40. In some piezoelectric motors 41,in accordance with embodiments of the present invention, at least onehole is formed in the body of vibrator 40 and/or at least one groove isformed on a narrow edge surface of vibrator 40. The at least one holeand/or at least one groove is formed to remove or reduce overlap thatthe excitation curve of the desired longitudinal frequency may have withan excitation curve of another resonant vibration mode of the vibrator.By reducing such overlap, energy coupled to unwanted vibration modes ofvibrator 40 is reduced and efficiency of operation of piezoelectricmotor 41 is improved.

Inset 54 of FIG. 1C schematically shows piezoelectric motors 300 and 302that are identical to piezoelectric motor 41 except for a hole 304 andgrooves 306 formed in or on their respective vibrators 40. Piezoelectricmotors 300 and 302 are assumed, by way of example, to operate byexciting a first longitudinal and second transverse vibration mode ofvibrator 40. A hole 304 located on axis 53 at a node of the secondtransverse vibration mode of piezoelectric vibrator 300 diverges theexcitation curves of the two resonant vibration modes. Hole 304 ispreferably located at the center of vibrator 40, which is a nodal regionof the second resonant vibration mode of vibrator 40. Grooves 306,optionally, in pairs located on opposite long edges of vibrator 40, alsodiverge the excitation curves of the resonant vibrations. The pattern ofholes and grooves on piezoelectric motors 300 and 302 are by way ofexample and other patterns, in accordance with other embodiments of thepresent invention, are possible and can be advantageous.

FIG. 1D schematically shows another method for coupling motors 41, orvariations thereof, to a blade head 22. In FIG. 1D piezoelectric motors41 are coupled to a surface region of a coupling disc 64. A force 52generated using methods known in the art operates on each piezoelectricmotor 41 to resilient press its friction nub 43 to the surface ofcoupling disc 64. The motion of friction nubs 43 is similar to themotion of friction nubs 43 shown in FIG. 1C and coupling disc 64 andblade head 22 are rotated around axis 36.

FIG. 1E schematically shows a partial cutaway view of a shaver 63comprising two rotary blade heads 22. Each rotary blade head 22 ismounted so that its cutting blades 24 rotate directly beneath a foil 65of shaver 63. Cutting blades 24 are shown as seen through foils 65. Insome embodiments of the present invention, each of rotary blade heads 22is connected to a coupling disc 64, as shown in FIG. 1B, and isoptionally driven by a piezoelectric motor 57 similar to piezoelectricmotor 56 shown in inset 54 of FIG. 1A. Piezoelectric motor 57 isidentical to piezoelectric motor 56 except for holes 61 that are formedin the body of the motor's vibrator to improve the efficiency of themotor and slight modifications to electrodes 58 and 60 required toaccommodate the holes. A driving circuit 67 electrifies three-quarterelectrodes 58 of both piezoelectric motors 57 comprised in shaver 63 torotate blade heads 22.

FIGS. 2A–2E schematically show various configurations of rotary bladeheads of a shaver (not shown) coupled to piezoelectric motors, inaccordance with embodiments of the present invention.

FIG. 2A shows a rotary blade configuration 68 comprising three rotaryblade heads 22. In some embodiments of the present invention rotaryblade heads 22 are mounted in the shaver using methods known in the artso that their respective axes of rotation 36 are parallel andequidistant from each other. Points of intersection of the axes 36 witha common plane perpendicular to the axes therefore define vertices of anequilateral triangle, which is inscribed in a configuration circle 70 ofblade heads 22. The equilateral triangle is a convex equilateralconfiguration polygon of blade heads 22. The center of configurationcircle 70 is indicated by a circled cross hair 72.

A piezoelectric motor 74 is mounted between each pair of blade heads 22.Piezoelectric motors 74 are, optionally, similar to piezoelectric motorsshown in FIGS. 1A–1E or variants thereof and each piezoelectric motor 74comprises a relatively thin piezoelectric vibrator 73. However, eachpiezoelectric motor 74 comprises two friction nubs 48 instead of, as inpiezoelectric motors shown in FIGS. 1A–1E, only one friction nub 48.Long axis 53 of each piezoelectric motor 74 is preferably coincidentwith a chord of configuration circle 70 and substantially intersectsaxes of rotation 36 of the two rotary blade heads 22 between which thepiezoelectric motor is located. Each friction nub 48 of a piezoelectricmotor 74 contacts a cylindrical coupling surface 34 of a different oneof blade heads 22 between which the piezoelectric motor is mounted. Aresilient force, represented by a block arrow 76, urges axis of rotation36 of each blade head 22 towards center 72 of configuration circle 70.Forces 76 are generated using methods known in the art and theirmagnitudes are substantially equal. Each coupling surface 34 is therebyresiliently pressed with a substantially same magnitude force to each offriction nubs 48 with which it is in contact. Preferably, eachpiezoelectric motor 74 is secured in place by structural elements thatgrasp the piezoelectric motor at nodal points of its vibrator 73. Insome embodiments of the present invention long axis 53 is slightlydisplaced or rotated from the chord of the circle. The displacementgenerally tends to decrease wear of friction nubs 48 and may improvetransfer of energy to blade heads 22.

In order to rotate a rotary blade head 22 both piezoelectric motors 74that are coupled to coupling surface 34 of the rotary blade head mustcooperate to rotate the coupling surface in the same clockwise orcounterclockwise direction. In some embodiments of the presentinvention, this is accomplished by electrifying electrodes ofpiezoelectric motors 74 to excite a same vibration mode in all themotors. When a piezoelectric motor 74 is excited, its two friction nubsvibrate with elliptical motions in a same clockwise or counterclockwisedirection. The phases of their respective vibrations are however 180°out of phase. As a result, each piezoelectric motor 74 rotates the twocoupling surfaces 34 to which it is coupled in a same counterclockwiseor clockwise direction respectively. Therefore, if all piezoelectricmotor 74 are excited to vibrate with a same vibration mode, they allrotate the coupling surfaces to which they are coupled in a samedirection.

Whereas all piezoelectric motors 74 are optionally excited to vibratewith a same vibration mode, in some embodiments of the presentinvention, vibration modes in piezoelectric motors 74 coupled to a samecoupling surface 34 are out of phase with each other. As a result, eachof piezoelectric motors 74 that is coupled to a same coupling surface 34rotates the coupling surface at different times. Torque applied to thecoupling surface 34 by the piezoelectric motors 74 is applied in morefrequent impulses than in a case in which both piezoelectric motors 74rotate the coupling surface simultaneously. Energy is transmitted frompiezoelectric motors 74 to each coupling surface 34 and its rotary bladehead 22 generally more smoothly than if vibration modes in piezoelectricmotors 74 are in phase.

In FIG. 2A it is assumed that piezoelectric motors 74 are excited sothat each of friction nubs 48 executes counterclockwise ellipticalvibrations. The direction in which a friction nub 48 rotates a couplingsurface 34 to which it is coupled is indicated by the direction of anarrow 78 that is located near the friction nub.

FIG. 2B shows configuration 68 shown in FIG. 2A comprising apparatus forgenerating forces 76 that press axes of rotation 36 towards center 72 ofconfiguration circle 70, in accordance with an embodiment of the presentinvention. In FIG. 2B, each shaft 30 is mounted in the shaver usingmethods known in the art that enable the shaft to slide or bend in aradial direction towards center 72. Each shaft 30 is mounted with abearing 31 that is freely rotatable about the shaft on which the bearingis mounted. In some embodiments of the present invention, each bearing31 has a grooved rim 33. A band or “O-ring” 35 formed from an elasticmaterial is preferably stretched taught and positioned in grooves 33 soas to loop around all bearings 31 and generate forces 76. Alternativemethods of generating forces 76 will readily occur to persons of theart. For example each of bearings 31 can be constructed with a rimhaving eyeholes close to its perimeter. Forces 76 are generated bytensed springs connected between adjacent bearing rims using theeyeholes. In some embodiments of the present invention grooves areformed in each of the shafts or in a circularly cylindrical surfacerigidly attached to each shaft. As in the case in which shafts 30 arefitted with grooved bearings a stretched O-ring or elastic band ispositioned to loop around all the grooves to generate forces 76. Whenpiezoelectric motors 74 rotate shafts 30 the O-ring or elastic bandrotates with the shafts in much the same way that a fan belt rotatesaround pulley wheels to which it is coupled in a car. In someembodiments of the present invention shafts 30 are flexible and a springaction of each shaft 30 generates a force 76 that maintains a flexiblepressure on each of friction nubs 48 with which the shaft's couplingsurface 32 is in contact.

Whereas rotary blade configuration 68 comprises three rotary blade heads22 and three piezoelectric motors 74, it is possible, in accordance withembodiments of the present invention, to have similar configurationswith different numbers of rotary blade heads 22 and piezoelectric motors74 and such configurations can be advantageous. Limited only by space, aconfiguration similar to configuration 68 can have any number of bladeheads 22 interleaved with piezoelectric motors 74 on configurationcircle 70. FIG. 2C shows a configuration 69 comprising four rotary bladeheads 22 and FIG. 2D shows a configuration 71 comprising two rotaryblade heads 22 interleaved with a single piezoelectric motor 74.

FIGS. 2A–2D schematically show symmetric configurations of blade heads22 that have a convex equilateral polygon for a configuration polygonand thereby a configuration circle within which the configurationpolygon is inscribed. Embodiments of the present invention are notlimited to such highly symmetric configurations. Parallel axes ofrotation 36 of a plurality of blade heads 22 can, in accordance withembodiments of the present invention, define vertices of a configurationpolygon that is neither equilateral nor convex or that may beequilateral and not convex or convex and not equilateral.

FIG. 2E schematically shows, by way of example a configuration 310 offive blade heads 22 having axes 36 that define a configuration polygon312 having vertices labeled V₁–V₅. Polygon 312 is a non-convexequilateral pentagon. In FIG. 2E, besides polygon 312, for simplicity ofpresentation only blade heads 22 and their axes of rotation 36 areshown. As in FIGS. 2A–2D, at least one piezoelectric motor (not shown),optionally similar to piezoelectric motor 76 (FIGS. 2A–2D), is mountedbetween each pair of adjacent blade heads 22. Each of two friction nubson the at least one piezoelectric motor contacts a coupling surface ofeach blade head between which the piezoelectric motor is mounted.Preferably, a force operates to urge each axis 36 in a direction of thebisector of the smaller of the two angles defined by sides ofconfiguration polygon 312 that meet at the vertex of polygon 312 atwhich the axis is located. The smaller of the two angles defined byadjacent sides of polygon 312 that meet at vertices V₁–V₅ are labeledrespectively α₁–α₅. The forces that operate on axes 36 at vertices V₁–V₅are indicated by block arrows labeled F₁–F₅ respectively. For a givenset of angles α₁–α₅, magnitudes of forces F₁–F₅ can be readily bedetermined so that there is a net zero force operating on each axis ofrotation 36. The magnitudes so determined result in each friction nub(not shown) of the at least one piezoelectric motor mounted betweenpairs of adjacent blade heads 22 being pressed with a same force to itsrespective coupling surface.

Whereas FIGS. 2A–2D show only one piezoelectric motor 74 between tworotary blade heads 22 it is possible, in accordance with embodiments ofthe present invention, to have more than one piezoelectric motor betweentwo blade heads 22. Two or more piezoelectric motors 78 can be stackedvertically between any two rotary blade heads 22 and coupling wheels 32can be made wider, or more coupling wheels 32 can be added, to couplerotary blade heads 22 to the added piezoelectric motors. This may beadvantageous for example when rotary blade heads 22 are closely spacedand more power is required to drive them than can be provided by asingle relatively small piezoelectric motor positioned between adjacentrotary blade heads.

The method of coupling piezoelectric motors 74 to rotary blade heads 22shown in FIGS. 2A–2D tends to be efficient at extracting energy frompiezoelectric motors to drive rotary blade heads 22. The only structuralelements that are in contact with vibrating surface regions ofpiezoelectric motors 74 are shafts 30 that the piezoelectric motors areintended to move. Structural elements that secure a piezoelectric motor74 in place preferably contact the piezoelectric motor at nodal regionsof the motor so that little energy is transmitted to them from themotor. As a result, each piezoelectric motor 74 transmits energysubstantially only to shafts 30 to which it is coupled.

This is in contrast to prior art systems in which a resilient structuralelement that presses a piezoelectric motor to a body that it movesgenerally contacts a surface region of the piezoelectric motor thatvibrates when the motor is energized. The structural element thereforeabsorbs energy from the piezoelectric motor when the motor is operatingand reduces the efficiency with which the motor moves the body to whichit is coupled.

In some embodiments of the present invention, blade heads 22 rotate inonly one direction and motors 74 are formed with a three-quarterelectrode and a single quadrant electrode instead of four quadrantelectrodes as shown in FIGS. 2A–2D. The use of three-quarter electrodesfor exciting vibration modes in piezoelectric motors 74 generallyfurther improves the efficiency with which energy is transmitted toblade heads 22 using configurations and methods shown in FIGS. 2A–2D.

In some embodiments of the present invention piezoelectric motors 76 aresimilar to a piezoelectric motor shown in FIGS. 1C and 1D that comprisesan “asymmetric” friction nub 43, except that instead of comprising asingle asymmetric friction nub the motor comprises two asymmetricfriction nubs. FIG. 2F schematically shows a piezoelectric motor 314similar to piezoelectric motors shown in FIGS. 1C and 1D. Piezoelectricmotor 314 optionally comprises a relatively thin rectangularpiezoelectric vibrator 40 having an axis 53 and optionally a singlelarge electrode 39 on each of its planar face surfaces 42. In someembodiments of the present invention two asymmetric friction nubs 43 aremounted on opposite short edges 50 of vibrator 40. Asymmetric nubs 43are preferably substantially identical and “point” in oppositedirections with respect to axis 53. When longitudinal vibration parallelto axis 53 are excited in piezoelectric vibrator 40, friction nubs 43execute elliptical oscillations in the same direction (i.e. bothelliptical motions are either clockwise or counterclockwise) that are180° out of phase.

FIGS. 3A and 3B schematically show configurations of rotary blade headsas they would be mounted in a shaver in which each rotary blade isdriven by its own piezoelectric motor, in accordance with embodiments ofthe present invention.

FIG. 3A shows a rotary blade head configuration 80 comprising threerotary blade heads 22 each of which is coupled to a different optionallyidentical piezoelectric motor 20 similar to a piezoelectric motor shownin FIGS. 1A–1D, variations thereof or other suitable motors known in theart. The choice of three blade heads 22 is by way of example and aconfiguration similar to configuration 80 can, in accordance with anembodiment of the present invention, comprise a different number ofrotary blade heads 22 and such a different number can be advantageous.

Rotary blade heads 22 have axes of rotation 36 that are optionallyparallel and equidistant from each other and define an equilateraltriangle and a configuration circle 70. The center of configurationcircle 70 is indicated by circled cross hairs 72. Each rotary blade head22 is preferably attached to a coupling wheel 32 having a couplingsurface 34. Coupling wheels 32 are optionally coplanar. Each ofpiezoelectric motors 20 has short edge surfaces 50 and 51, a long axis53 and optionally, a friction nub 48.

A piezoelectric motor 20 to which a rotary blade head 22 is coupled ismounted in the shaver, using methods known in the art, so that its longaxis 53 is substantially coincident with a radius (not shown) of circle70 that intersects rotation axis 36 of the rotary blade head. Shaft 30is preferably rigidly mounted in the shaver, using methods known in theart so that the position of shaft 30 and thereby axis 36 issubstantially fixed. In some embodiments of the present invention,piezoelectric motor 20 is situated between center 72 of circle 70 andcoupling wheel 32 of blade head 22. A resilient force, represented by ablock arrow 76, presses against edge surface 51 of piezoelectric motor20. Force 76 urges piezoelectric motor 20 along its long axis 53 so thatfriction nub 48 presses against coupling surface 34 attached to rotaryblade head 22. In some embodiments of the present invention edge surface51 is substantially rigidly held in position and resilience of shaft 30is used to press coupling surface 34 to friction nub 48.

In some embodiments of the present invention, resilient forces 76 aregenerated by a circular disc 82 formed from an elastic material. Disc 82is mounted to the shaver (not shown) using methods known in the art sothat its center is substantially rigidly positioned at center 72 ofconfiguration circle 70. Preferably, disc 82 and piezoelectric motors 20are coplanar. Preferably, the distances of short edges 51 of allpiezoelectric motors 20 from center 72 of configuration circle 70 aresubstantially equal. The radius of disc 82 is larger than the distancesof short edges 51 of piezoelectric motors 20 from center 72. As a resultdisc 82 is radially compressed at points where it contacts an edgesurface 51 of a piezoelectric motor 20. The compression generatesresilient forces 76. In some embodiments of the present invention disc82 is not rigidly positioned at center 72 of configuration circle 70,but disc 82 is aligned at or close to center 72 by pressure from thepiezoelectric motors 20 against which disc 82 presses.

Other methods of generating forces 76 will readily occur to persons ofthe art. For example disc 82 can be replaced by a configuration ofsprings using methods known in the art.

FIG. 3B shows a configuration 84 of rotary blade heads 22 andpiezoelectric motors 20, (or variations thereof or other suitable motorsknown in the art) in accordance with an embodiment of the presentinvention. Configuration 84 is similar to configuration 80, however inconfiguration 84 coupling wheels 32 are not coplanar. Each couplingwheel 32 is located on a different plane. (Rotary blade heads 22 are ofcourse coplanar or substantially coplanar and are connected to theirrespective coupling wheels by different length shafts 30.) Piezoelectricmotors 20 are not coplanar and extend past center 72 of configurationcircle 70. Resilient forces 76 urge piezoelectric motors 20 along theirlong axes 53 to press their respective friction nubs 48 to couplingwheels 32 to which they are coupled. For a same radius configurationcircle 70, piezoelectric motors 20 in configuration 84 can be larger andlonger than piezoelectric motors 20 used in configuration 80 shown inFIG. 3A. Alternatively, for piezoelectric motors 20 in configurations 84and 80 having a same length, configuration circle 70 in configuration 84can be smaller than configuration circle 70 in configuration 80, i.e.rotary blade heads 22 can be closer together in configuration 84.

It should be noted that whereas coupling wheels 32 in FIG. 3B are notcoplanar, it is possible, in accordance with embodiments of the presentinvention, to couple non-coplanar piezoelectric motors 20 to coplanarcoupling wheels 32 by making the coupling wheels wider. It should alsobe noted that whereas piezoelectric motors 20 in FIGS. 3A and 3B arepositioned so that their respective axes 53 are along radii ofconfiguration circle 70, other orientations of piezoelectric motors 20,in accordance with embodiments of the present invention, are possibleand can be advantageous. For example axes 53 can extend along tangentsor arcs of configuration circle 70. Furthermore, whereas in FIG. 3B andpreceding figures, coupling surfaces 34 are surfaces of coupling wheels32 attached to shafts 30, coupling surfaces 34 can be a surface regionsof shafts 30 in all embodiments of the present invention requiring acoupling surface 34.

FIG. 4 schematically shows a configuration 86 of rotary blade heads 22for a shaver that are driven by a planetary gear transmission, inaccordance with an embodiment of the present invention.

Configuration 86 comprises three (by way of example) rotary blade heads22 each one of which is connected to a different gear 88. Gears 88 areplanet gears of a planetary gear transmission 90 comprising an annulusgear 92 which is coupled to planet gears 88 using methods known in theart.

In some embodiments of the present invention annulus gear 92 comprisesan apron 94 having an internal surface 96 to which at least onepiezoelectric motor 20 is coupled. Optionally, piezoelectric motor 20 issimilar to piezoelectric motor 20 shown in FIG. 1A (or to anotherpiezoelectric motor shown in FIGS. 1A–1C, or other suitablepiezoelectric motor known in the art) and comprises a friction nub 48which is resiliently pressed to surface 96 of apron 94. Optionallysurface 96 is covered with a layer of wear resistant material. When theshaver is in operation piezoelectric motor 20 turns annulus gear 92 andthereby planet gears 88 and rotary blade heads 22. It should be notedthat annulus gear 92 can be driven by a piezoelectric motor similar topiezoelectric motor 74 (FIGS. 2A–2D) or motor 314 (FIG. 2F) having twofriction nubs that engage surface 96 of apron 94 at opposite ends of adiameter of surface 96.

Whereas FIG. 4 shows a configuration comprising three rotary bladeheads, configurations of rotary blade heads driven by a planetary geartransmission can, in accordance with embodiments of the presentinvention, comprise a different number of blade heads. Furthermoreplanetary transmissions in accordance with embodiments of the presentinvention having configurations different from that shown in FIG. 4 arepossible and can be advantageous. For example, a “planetaryconfiguration” of rotary blade heads, in accordance with an embodimentof the present invention, might by way of example comprise five rotaryblade heads. Each of four of the rotary blade heads might be attached toa planet gear while a fifth rotary blade head is attached to a centralsun gear that is coupled to each of the planet gears. The planetarytransmission might not comprise an annulus gear to drive the gearsattached to the blade heads. Instead, the planet gears might be drivenby the sun gear, which is rotated by at least one piezoelectric motor.

FIG. 5 schematically shows a rotary blade head 100, in which cuttingblades are parallel to an axis of rotation of the blade head, coupled toa piezoelectric motor 20, in accordance with an embodiment of thepresent invention. Piezoelectric motor 20 shown in FIG. 5 is, by way ofexample, similar to piezoelectric motor 20 shown in FIG. 1A.

Rotary blade head 100 optionally comprises at least two circularparallel hubs 102 and 104 preferably having equal radii and a commonaxis of rotation 106. Optionally, a plurality of cutting blades 108having cutting edges 110 extend from hub 102 to hub 104. In someembodiments of the present invention, cutting edges 110 are straight andsubstantially parallel to axis of rotation 106. In some embodiments ofthe present invention, cutting edges 110 are slightly skewed withrespect to axis of rotation 106. In some embodiments of the presentinvention cutting edges are convex. In FIG. 5 cutting edges 110 ofcutting blades 108 are straight and parallel to axis of rotation 106.

Hub 102 optionally comprises a coupling wheel 103 having a couplingsurface 105 to which piezoelectric motor 20 is coupled. Whenpiezoelectric motor 20 is activated it rotates coupling wheel 100 andthereby cutting blades 108 about axis of rotation 106.

FIG. 6A schematically shows an oscillatory blade head 120 for use in ashaver having cutting blades that are moved with a rotational,oscillatory motion, coupled to a piezoelectric motor 20 in accordancewith an embodiment of the present invention.

In some embodiments of the present invention, oscillatory blade head 120comprises a cylindrical arc surface 122 that functions as a couplingsurface and two cylindrical “arc” struts 124 and 126, all having acommon axis of rotation 128. A plurality of cutting blades 130,preferably having cutting edges 132 parallel to axis of rotation 128,are supported by cylindrical struts 124 and 126.

Piezoelectric motor 20 is optionally similar to piezoelectric motor 20shown in FIG. 1A and comprises a large electrode (not shown), 4 quadrantelectrodes 46 and a friction nub 48. A resilient force 76 operates onpiezoelectric motor 20 to press friction nub 48 to coupling surface 122.Optionally, diagonally opposite quadrant electrodes 46 are electricallyconnected together to form first and second electrode pairs 117 and 119respectively, of diagonally connected electrodes. A driving circuit 121is connected to the large electrode and first and second electrode pairs117 and 119 by power lines 123. Power from driving circuit 121 isalternately switched to first electrode pair 117 and second electrodepair 119 to alternately electrify the first and second electrode pairswith respect to the large electrode and alternately generate therebyclockwise and counterclockwise elliptical vibrations in friction nub 48.The clockwise and counterclockwise elliptical vibrations rotate couplingsurface 122 and thereby cutting blades 130, with a back and forthoscillatory motion about axis of rotation 128.

In some embodiments of the present invention driving circuit 121 is adriving circuit of a type described in PCT Application PCT/IL99/00520and switching between first and second pairs of diagonally connectedelectrodes 46 is, optionally, accomplished using methods described inthis PCT Application. Other driving circuits and methods of electrifyingelectrodes known in the art may be used.

Whereas electrodes 46 are shown in FIG. 6A as being electrified indiagonal pairs, electrodes 46 may, in accordance with an embodiment ofthe present invention, be electrified to generate alternating directionelliptical vibrations using other combinations of electrodes.Furthermore voltage waveforms different from harmonic waveforms may beused to electrify electrodes 46. Such other combinations of electrodes46 and voltage waveforms different from harmonic waveforms aredescribed, as noted above, in U.S. Pat. No. 5,616,980.

Power supply 121 and methods for electrifying electrodes 46 toalternately generate clockwise and counter clockwise vibrations infriction nub 46 are suitable for use in any preferred embodiment of thepresent invention that requires generating motion in two opposite andparallel directions.

FIG. 6B schematically shows another oscillatory blade head 140 formoving cutting blades in a shaver (not shown) with a rotationaloscillatory motion.

Oscillatory blade head 140 comprises an arc surface 142 that functionsas a coupling surface and two parallel cylindrical arc struts 144 and146 all having a common axis of rotation 148. A plurality of cuttingblades 150 having cutting edges 152 that are optionally parallel to axisof rotation 148 are supported by cylindrical struts 144 and 146. Apiezoelectric motor 20, similar to and operated in the same manner aspiezoelectric motor 20 shown in FIG. 6A is urged by resilient force 76in a direction so that its friction nub 48 presses against couplingsurface 142. Pairs of diagonally connected quadrant electrodes 46 arepreferably electrified with an AC voltage to rotate coupling surface 142and thereby cutting blades 150 with a back and forth oscillatory motionabout axis of rotation 148.

FIG. 7 schematically shows an oscillatory blade head 160 for movingcutting blades in a shaver with a linear oscillatory motion, coupled toa piezoelectric motor 20, in accordance with an embodiment of thepresent invention.

Oscillatory blade head 160 optionally comprises a planar support plate162. A plurality of optionally parallel cutting blades 164 are attachedin a linear array on a top surface 166 of support plate 162. The lineararray has an array axis 168 shown with a dashed line.

Piezoelectric motor 20 is optionally similar to and operated in similarmanner as piezoelectric motor 20 shown in FIGS. 6A and 6B. A resilientforce 76 urges piezoelectric motor 20 in a direction so that itsfriction nub 48 presses against a surface region of a bottom surface 170of support plate 162.

In some embodiments of the present invention pairs of diagonallyconnected quadrant electrodes 46 are electrified with an AC voltage tovibrate friction nub 48 alternately with clockwise and counterclockwiseelliptical motion. The motion of friction nub 48 moves oscillatory bladehead 160 back and forth parallel to array axis 168 with a linearoscillatory motion in directions indicated by double arrowhead line 172.

It should be noted that piezoelectric motor 20 shown in FIGS. 6A–7 issimilar to piezoelectric motor 20 shown in FIG. 1A by way of example.Any friction coupled piezoelectric motor operable to rapidly oscillate amoveable body to which it is coupled can be used in place of motor 20,in accordance with an embodiment of the present invention. In someembodiments of the present invention, a piezoelectric motor used inplace of piezoelectric motor 20 is similar to a piezoelectric motorshown in FIGS. 1A–1D.

FIG. 8 schematically shows a resonant blade head 180 driven by apiezoelectric motor 182, for moving cutting blades in a shaver (notshown) by exciting resonant vibrations in the cutting blades, inaccordance with an embodiment of the present invention. FIG. 8 showsresonant blade head 180 in a perspective side view.

Resonant blade head 180 comprises a base plate 184 having a top surface186 to which are mounted in a linear array, a plurality of optionallyparallel “resonant” cutting blades 188 having cutting edges 190. Adirection of the linear array is defined by an array axis 192perpendicular to the planes of cutting blades 188. In some embodimentsof the present invention a “strike” plate 194 is mounted to a bottomsurface 196 of base plate 184. The plane of strike plate 194 ispreferably perpendicular to array axis 192. A resilient “backstop” block185 mounted to the shaver using methods known in the art limits motionof base plate 184 parallel to array axis 192 in the direction of force76.

Resonant cutting blades 188 are designed, using methods known in theart, to have a resonant vibration mode characterized by a desiredfrequency. When the resonant vibration mode is excited, it causescutting edges 190 to vibrate back and forth in directions indicated bydouble arrowhead lines 200 at the frequency of the resonant vibrationmode. The frequency of the resonant vibration mode is determined by themass distribution of the cutting blades and the coefficient ofelasticity of the material from which they are made. An amplitude ofmotion of cutting edges 190 is determined by the mass distribution,material elasticity, a damping factor of the resonant vibration and arate at which energy is supplied by piezoelectric motor 182 to theresonant vibration mode. In some embodiments of the present invention,the frequency of vibration of cutting edges 190 is in a range from50–250 Hz and the amplitude of vibration is in a range from 0.5 to 2 mm.Preferably, the elasticity of material from which backstop plate 185 isformed is such that motion of base plate 184 parallel to array axis 192has a resonant frequency substantially equal to the resonant frequencyof cutting blades 188.

In FIG. 8, cutting blades 188 are shown, in accordance with anembodiment of the present invention, formed with a window 202. For agiven constant thickness of cutting blades 188 and a given elasticity ofthe material from which cutting blades 18 are formed, the size and shapeof window 202 determines the mass distribution of cutting blades 188 andthereby the resonant frequency of cutting blades 188. Other methods fordetermining a resonant vibration frequency of cutting blades 188, inaccordance with an embodiment of the present invention, will occur topersons of the art.

The resonant vibration mode is excited when strike plate 194 is coupledto a force that moves it back and forth along array axis 192 with afrequency close to the frequency of the resonant vibration mode ofcutting blades 188. The force is provided by piezoelectric motor 182.

Piezoelectric motor 182 is optionally similar in construction topiezoelectric motors shown in previous figures and comprises arelatively thin rectangular piezoelectric vibrator 203 having two largeplanar face surfaces 204, only one of which is shown in FIG. 8, and along axis 206. Optionally vibrator 203 is mounted with a cone shaped“concentrator” nub 205 formed from stainless steel or hard ceramic. Nub205 is pressed to strike plate 194 by a resilient force 76. Optionally,piezoelectric motor 182 comprises identical large electrodes 208 on bothof its planar face surfaces 204. (Only one of large electrodes 208 isshown in the perspective of FIG. 8).

When an AC voltage is applied between large electrodes 208,substantially only longitudinal vibrations parallel to long axis 206 ofpiezoelectric motor 182 are excited in the piezoelectric motor. Thelongitudinal vibrations generate vibrations in nub 205 in directionsindicated by double arrowhead line 210. These vibrations in nub 205 movestrike plate 194 parallel to array axis 192, to excite the resonantvibration of cutting blades 188. However, in order to couple energyefficiently into vibrations of piezoelectric motor 182 an AC voltagehaving a frequency close to the longitudinal resonant frequency ofpiezoelectric vibrator 203. The longitudinal resonant frequency ofpiezoelectric motor 182 is generally in a range from 10,000 to 100,000Hz. Frequencies in this range are much higher than the frequencyrequired to excite the resonant vibration mode of cutting blades 188. Asa result, the natural vibration frequencies of piezoelectric motor 182are not suitable for directly exciting the resonant vibration mode ofcutting blades 188. Therefore, in accordance with an embodiment of thepresent invention, in order to generate a suitable force for excitingthe resonant frequency of cutting blades 188, the applied AC voltage ismodulated by an envelope function having a frequency substantially equalto the resonant frequency of cutting blades 188. As a result of themodulation, vibratory motion of nub 205 generates a force on strikeplate 194 characterized by a frequency equal or close to the frequencyof the resonant vibration mode of cutting blades 188. In someembodiments of the present invention the modulation function is anharmonic function or a cyclical hat function generated by turning the ACvoltage on and off at the frequency of the resonant vibration mode ofcutting blades 188.

FIG. 9 schematically shows another resonant blade head 220 coupled to apiezoelectric motor 221, in accordance with an embodiment of the presentinvention.

Blade head 220 comprises a hub 222 to which are attached a plurality ofcutting blades 224 that extend radially away from hub 222. In someembodiments of the present invention cutting blades 224 comprise anarrow arm section 226 and a broader head section 228 so that cuttingblades 224 are more heavily weighted towards their free ends. Cuttingblades 224 preferably have cutting edges 230 located on their headsections 228. Blade head 220 is optionally rotationally symmetric aboutan axis of rotation 232 shown with a dashed line.

A shaft 234 connects blade head 220 to a strike plate 236. A backstopblock 238 limits motion of strike plate 236. Piezoelectric motor 221 isoptionally similar to and operates in the same manner as piezoelectricmotor 182 shown in FIG. 8. However in FIG. 9 impulses that piezoelectricmotor transmits to strike plate 236 generate an intermittent torque at aresonant frequency of cutting blades 224. The torque excites a resonantvibration in cutting blades 224 that causes their cutting edges to moveback and forth in directions indicated by double arrowhead lines 240.For a given magnitude of force applied to strike plate 236 the increasedweighting of cutting blades 224 toward their free ends increases theamplitude of motion of the cutting edges 230.

FIG. 10 schematically shows a wet shaver 250 in accordance with anembodiment of the present invention.

Wet shaver 250 optionally comprises a handle 252 a piezoelectric motor254 and a mounting plate 256. An optionally disposable razor blade 258having a cutting edge 260 is mounted to mounting plate 256 using methodsknown in the art.

Piezoelectric motor 254 is optionally mounted in a recess 262 in handle252. In some embodiments of the present invention, piezoelectric motor254 comprises a cone shaped nub 205 formed from steel or hard ceramicand is spring loaded using methods known in the art so that nub 205 isresiliently pressed to mounting plate 256. Piezoelectric motor 254optionally operates in similar fashion to the way that piezoelectricmotors 182 and 221 shown in FIGS. 8 and 9 respectively operate and whenenergized, substantially only longitudinal vibrations are excited inpiezoelectric motor 254. In some embodiments of the present invention,piezoelectric motor 254 is similar to low voltage piezoelectricmultilayer motors described in PCT Application PCT/IL99/00288 but,optionally, with all electrodes on layers in the motor being relativelylarge single electrodes that cover substantially all the area ofsurfaces of the layers on which they are located.

Piezoelectric motor 254 and circuits (not shown) and leads (not shown)in handle 252 that provide power to piezoelectric motor 254 arepreferably waterproofed with a coating of a suitable flexible waterresistant insulator. In addition or alternatively, recess 262 may be arecess in a suitable waterproof compartment of wet shaver 250 thatprevents moisture from reaching piezoelectric motor 254 and itsassociated leads and circuits. Optionally, nub 205 is a “replaceable”friction nub similar to replaceable friction nubs described in a PCTApplication entitled “Replaceable Friction Nub”, filed on even dateherewith in the Israel Receiving Office, the disclosure of which isincorporated herein by reference. Replaceable friction nubs described inthe PCT Application are designed so that they can be easily attached andremoved from a piezoelectric motor. By using a replaceable nub 205,piezoelectric motor 254 can be waterproofed first and nub 205 attachedlater, after waterproofing. This enables a better seal of the insulatingcoating to the motor and prevents the surface of nub 205 from beingdegraded by the coating.

The longitudinal vibrations in piezoelectric motor 254 move nub 205 backand forth with a linear vibratory motion in directions indicated bydouble arrowhead line 264. Mounting plate 256 is optionally attached tohandle 252 by a neck 266 (only a portion of which is shown in FIG. 10)having thin rectangular cross section. The long dimension of the crosssection of neck 266 is parallel to cutting edge 260 of razor blade 258.The shape of the cross section of neck 266 and the material from whichneck 266 is formed are chosen so that neck 266 is elastically bendableabout an axis parallel to the long dimension of the cross section andrelatively inflexible and rigid in other directions. Neck 266 istherefore bendable substantially only about an axis parallel to cuttingedge 260. The vibratory motion of nub 205 therefore generates rotaryvibratory motion of cutting edge 260 substantially only about an axisparallel to the cutting edge. The motion of cutting edge 260 isindicated by double arrowhead line 262. Preferably, vibratory motion 262has a frequency greater than 5,000 Hz. More preferably the vibratorymotion of cutting edge 260 has a frequency greater than 10,000 Hz. Mostpreferably, the frequency of vibratory motion 262 is greater than20,000. Preferably, handle 252, neck 266 and mounting plate 256 areformed as a single unit from metal or suitable plastic using methodsknown in the art.

Other methods known in the art for mounting razor blade 258 to handle252 that enables the motion of cutting edge 260 represented by lines 262are possible, in accordance with an embodiment of the present invention,and can be advantageous. For example mounting plate 256 can be attachedto handle 252 by a hinge and the plate biased by a flexible force thatmaintains the plate pressed against nub 205.

Wet shaver 250 is used for shaving preferably with water and a shavingcream in the same manner that prior art wet shavers are used. However,as a result of the vibrations in cutting edge 260 generated bypiezoelectric motor 254, wet shaver 250 provides a shave that issmoother than shaves provided by prior art shavers.

Motion of resonant cutting blades 188 and 228 shown in FIGS. 8 and 9respectively and razor blade 258 comprised in wet shaver 250 shown inFIG. 10 is generated by a piezoelectric motor preferably comprising aconcentrator nub that vibrates substantially along a single directionand impacts a strike plate. It is also possible, in accordance withpreferred embodiment of the present invention, to generate motion ofcutting blades 188, 288 and razor blade 228 using a piezoelectric motor20 having a friction nub 48 and coupling methods shown in FIGS. 6A and6B. The piezoelectric motor generates the desired motion by oscillatingthe resonant cutting blades or razor blade in similar manner to the wayin which piezoelectric motor 20 oscillates cutting blades attached tooscillating blade heads 120 and 140 shown in FIGS. 6A and 6B.

Whereas in FIG. 10 cutting edge 260 is moved perpendicular to itself, insome embodiments of the present invention, cutting edge 260 is movedwith a linear oscillatory motion back and forth parallel to itselfMovement of cutting edge 260 parallel to itself is optionallyaccomplished by connecting mounting plate 256 to handle 252 usingmethods known in the art so that plate 256 is moveable in the desireddirections. A piezoelectric motor oscillates mounting plate 256 back andforth parallel to cutting edge 260 in much the same way thatpiezoelectric motor 20 shown in FIG. 7 oscillates support plate 162.

FIGS. 11A–17 schematically show various configurations of piezoelectricstar motors and star motors driving shafts, in accordance withembodiments of the present invention. To prevent clutter, only somefeatures and elements of a plurality of identical features and elementsshown in FIGS. 11A–15 that are identified by a same numeral may belabeled with the numeral.

FIG. 11A shows a star motor 320 for driving three shafts. Star motor 320comprises three, optionally, identical, substantially rectangulardriving arms 322 that extend outwardly in radial directions indicated bydashed lines 324 from a common center 326. In some embodiments of thepresent invention driving arms 322 are identical and an angle betweenradial directions 324 of a pair of adjacent driving arms 322 is equal toan angle between radial directions 324 of any other pair of adjacentdriving arms 322. Lines 324 lie along long lines of symmetry of drivingarms 322 and therefore, where appropriate, will be referred to as “axes”324 of driving arms 320.

Star motor 320 comprises a single relatively thin planar piezoelectricvibrator 330 having two large parallel planar face surfaces 332 (onlyone of which is shown) and three rectangular shaped arms 334 that extendoutwardly along radial directions 324. Piezoelectric vibrator 330 isbonded to a similarly shaped base plate 340 having three rectangulararms 342 so that each driving arm 322 of the piezoelectric vibrator isbonded to an arm 342 of the base plate to form a driving arm 322 ofmotor 320. Base plate 340 is preferably formed from a non-piezoelectrichigh Q material. Preferably, base plate 340 is formed from a metal suchas aluminum or steel.

The base plate arm 342 and piezoelectric arm 334 of each driving arm 322are formed with a clearance hole or groove for receiving a shaft drivenby star motor 320. By way of example, in star motor 320 piezoelectricarms 334 are formed with clearance grooves 336 and base plate arms 342are formed with clearance holes 344. A dashed “centerline” 346 throughthe center of each clearance hole 344, perpendicular to the plane ofmotor 320, preferably intersects axis 324 of the driving arm 322 inwhich the hole is located at a point 350.

In some embodiments of the present invention, a friction nub 352 ismounted to each piezoelectric arm 334 on face surface 332 in a region ofa corner 354 of the arm. In some embodiments of the present inventionfriction nubs 352 are bonded to face surface 332 using adhesives andmethods known in the art. A line 356 (shown dashed) from the location ofa friction nub 352, perpendicular to the plane defined by centerline 346and axis 324 of the driving arm 322 on which the friction nub is locatedpreferably intersects the centerline. For convenience of presentation,in FIG. 11A axes 324 are shown located on planar face surface 332. As aresult, points 350 at which centerlines 346 and axes 324 intersect arealso the points at which lines 356 intersect centerlines 346. In someembodiments of the present invention, a single large electrode 360having a shape generally similar to that of piezoelectric vibrator 330is located on face surface 332. When an AC voltage difference is appliedbetween electrode 360 and base plate 340, each arm of piezoelectricvibrator 330 cyclically expands and contracts along a “longitudinal”direction parallel to its axis 324 with a frequency equal to thefrequency of the driving voltage. As a result friction nub 352 of eachdriving arm 322 moves back and forth in directions parallel to thedriving axis 324

However the material of base plate 340 does not in general exhibitsignificant expansion or contraction with generation of an electricfield in the material. Therefore, when a piezoelectric arm 334 is causedto expand and contract by the driving voltage, mechanical forces aregenerated in its driving arm 322 that cause the driving arm to bend sothat the piezoelectric side of the driving arm is respectively convexand concave. The bending motion causes friction nub 352 of driving arm322 to move “up and down” in directions perpendicular to the plane ofthe driving arm.

The (longitudinal) vibratory motion of a friction nub 352 parallel toaxis 324 of the driving arm 322 on which it is located and vibratorybending motion of the friction nub are used, in accordance withembodiments of the present invention, to impart motion to a moveableelement.

It is possible to operate star motor 320, in accordance with anembodiment of the present invention, by exciting longitudinal andbending vibrations in the motor with a driving voltage at frequenciesthat are not close to frequencies of resonant vibration modes of thedriving arms of the motor. However, preferably, the materials anddimensions of star motor 320 are chosen so that each driving arm 322 hasa resonant longitudinal vibration mode at a frequency that is close to afrequency of a resonant bending vibration mode of the driving arm.Preferably, the frequency of the driving voltage is close to thefrequencies of the longitudinal and bending vibration modes.

In some embodiments of the present invention, the frequency of thedriving voltage is chosen so that relative phase between thelongitudinal and bending vibrations excited in a driving arm 322 resultsin the driving arm's friction nub 352 vibrating with an ellipticalmotion. An ellipse 362 near friction nub 352 of each driving arm 322schematically represents elliptical motion excited in the friction nubby longitudinal and bending vibrations in the driving arm. Each frictionnub 352 moves clockwise around its ellipse 362, as seen from theposition of the friction nub. A curved arrow 364 indicates the directionof motion of each friction nub 352 around its ellipse 362.

In an example of an embodiment of the present invention, piezoelectriclayer 330 is formed from a high Q piezoelectric material and base plate340 is formed from aluminum. The thickness of piezoelectric layer 330 isabout 2 mm, the thickness of base plate 340 is about 1 mm and eachdriving arm is about 6.3 mm wide and about 12.6 mm long. For thesedimensions and an appropriate high Q piezoelectric material, in someembodiments of the present invention, a first longitudinal resonantvibration mode and a third resonant bending vibration mode of eachdriving arm 322 are used to generate motion of friction nubs 352. Insome embodiments of the present invention, the longitudinal vibrationmode has a resonant frequency of about 61.4 kHz and the bendingvibration mode has a frequency of about 58.94 kHz.

In some embodiments of the present invention, the motion of a frictionnub 352 is used to drive a shaft 372 of a type schematically shown ininset 370 of FIG. 11A. Shaft 372 is formed with or attached to acoupling disc 374 having large surfaces 376, one of which is pressed toa friction nub 352 to couple motion of the friction nub to the disc andthereby to the shaft.

Whereas star motor 320 shown in FIG. 11A comprises a piezoelectricvibrator 330 fabricated as a one-piece “unitary” vibrator, some starmotors in accordance with embodiments of the present invention comprisea composite vibrator having components formed from non-piezoelectricmaterials.

FIG. 11B shows a star motor 500 similar to star motor 320 that comprisesa composite vibrator 502 mounted to a base plate 340 instead of aunitary vibrator 330. Composite vibrator 502 comprises a thinpiezoelectric vibrator 504 having arms 506 each of which is bonded to anend piece 508, shown shaded) formed from a non-piezoelectric material.Each end piece 508 is optionally integrally formed with a friction nub352 and a groove 336 (or hole) for receiving a shaft driven by starmotor 500. End pieces 508 are preferably fabricated from a hard wearresistant material such as Alumina, steel or PEEK. As in the case ofunitary vibrator 330, composite vibrator 502 is shown, by way ofexample, having a single large electrode 360. Whereas unitary vibrator330 and composite vibrator 502 are similar in shape and functionsimilarly, it can be cheaper and easier to fabricate a compositepiezoelectric vibrator of a type shown in FIG. 11B for use in a starmotor rather than a one piece unitary vibrator 330 of a type shown inFIG. 11A.

FIG. 11C schematically shows star motor 320 being used in a shaver (notshown), in accordance with an embodiment of the present invention, todrive three shafts 372 of a type shown in inset 370 of FIG. 11A. Eachshaft 372 is mounted with a rotary blade head 380 of the shaver.

Star motor 320 and shafts 372 are mounted in an appropriate supportstructure (not shown) so that each shaft 372 is positioned in a hole 344of a driving arm 322 of motor 320. The axis of the shaft 372 iscoincident with centerline 346 (FIG. 11A) of the hole 344 and a largesurface 376 of its disc 374 is resiliently pressed to friction nub 352of the driving arm. Elliptical motion of friction nub 352 generates atorque that rotates coupling disc 374 and shaft 372 and thereby rotaryblade head 380. Because friction nub 352 is located along line 356,(FIG. 11A) which is perpendicular to the plane formed by centerline 350of hole 344 and axis 324, substantially all force applied by thefriction nub to disc 374 is perpendicular to a radius of the disc. As aresult, substantially all force applied by friction nub 352 to couplingdisc 374 parallel to the plane of the disc generates a torque about theaxis of shaft 372 on the disc and transmission of torque to couplingdisc 374 by the driving arm 322 is relatively efficient.

Direction of rotation of shafts 372 in FIG. 11C are indicated by curvedarrows 382. For the configuration of star motor 320 shown in FIG. 11Aall the shafts rotate clockwise. If friction nubs 352 were located onthe corners of their respective driving arms 322 opposite to corners 354on which they are shown in FIG. 11A, shafts 372 would rotatecounterclockwise.

Shaft 372 and rotary blade head 374 coupled to the foremost driving arm322 of star motor 320 are partially cut away to show details of theposition of the shaft and contact of its coupling disc 374 with thedriving arm's friction nub 352.

It is to be noted that whereas holes 344 are described as clearanceholes, in some embodiments of the present invention, holes 344 are notclearance holes. Instead they are formed with a suitable radius, orfitted or formed with an appropriate structure so that they can hold ashaft 372 and function as a bearing for the shaft. In some embodimentsof the present invention, holes 344 are fitted with bearings to holdshafts 372.

Whereas in FIG. 11C one star motor 320 is shown driving shafts 372, insome embodiments of the present invention, two star motors of a typeshown in FIGS. 11A and 11C are used to drive the shafts.

FIG. 12A schematically shows shafts 372 being driven by a star motor 320such as shown in FIGS. 11A and 11C and a star motor 390 having drivingarms 392, in accordance with an embodiment of the present invention.Star motor 390 is a mirror image of star motor 320 in a plane parallelto the plane of motor 320 that passes through the centers of couplingdiscs 374.

Coupling discs 374 are sandwiched between motor 320 and mirror imagemotor 390 so that a friction nub 352 of each star motor resilientlypresses on each disc from opposite sides of the disc. The foremostdriving arm 392 of mirror image star motor 390 and shaft 372, rotaryblade head 380 and coupling disc 374 coupled to the foremost driving arm392 of motor 390 are partially cut away to reveal details of coupling ofthe shaft to the two motors. The cutaway features show friction nubs 352of star motor 320 and its mirror image star motor 390 pressing onopposite sides of coupling disc 374.

Various configurations of elastic elements and other support elements,in accordance with embodiments of the present invention are used tomaintain friction nubs 352 of piezoelectric motors 320 and 390resiliently pressed to coupling discs 374 of shafts 372. FIG. 12Bschematically shows an example, in accordance with an embodiment of thepresent invention, of a configuration of elastic and other supportelements used to resiliently press piezoelectric motor 390 topiezoelectric motor 320 and thereby friction nubs 352 to theirrespective coupling discs 374. In FIG. 12 B rotary blade heads 380 arenot shown to prevent clutter.

In FIG. 12B, piezoelectric motor 320 is supported by a support plate520. Each driving arm 322 of piezoelectric motor 320 rests on an,optionally rigid, pedestal 522 on support plate 520. Preferably, eachpedestal 522 contacts its respective driving arm 322 at a region of thedriving arm that is a nodal region for vibration modes of piezoelectricmotor 320 that are used to drive shafts 372. For each driving arm 392 ofpiezoelectric motor 390, optionally, a bracket 524 extends from supportplate 520 and loops around the driving arm. A spring 526, or otherappropriate elastic element, is supported by bracket 524 so that thespring resiliently presses on the driving arm 392. Preferably, spring526 presses on driving arm 392 at a location that is a nodal region ofthe driving arm. Brackets 524 are cutaway, where appropriate, to showpedestals 522 and springs 526.

In some embodiments of the present invention, a bracket 530 extends fromsupport plate 520 and loops around each driving arm 392 of piezoelectricmotor 390 at the location of the shaft 372 that is driven by the drivingarm. Bracket 530 is formed with a clearance hole 532 through which shaft372 passes. A spring 534, or other suitable elastic element, throughwhich shaft 372 passes is supported by bracket 530 so that the springresiliently presses on the end of the driving arm 392 in the region ofthe shaft.

Springs 526 and 530 function to resiliently press piezoelectric motor390 to piezoelectric motor 320 and thereby to press friction nubs 352 ofboth motors to coupling discs 374. Forces applied by springs 524 and 530that operate to press piezoelectric motors 390 to piezoelectric motor320 also operate, via contact of friction nubs 352 with coupling discs374 to keep piezoelectric motor 320 resiliently pressed to pedestals522.

In some embodiments of the present invention, springs or other elasticelements, are also positioned between piezoelectric motor 390 andpiezoelectric motor 320 to resiliently press piezoelectric motor 320 topedestals 522. In some embodiments of the present invention, to presspiezoelectric motor 320 to pedestals 522, a spring is positioned betweeneach driving arm 322 of piezoelectric motor 320 and its opposite, mirrorimage driving arm 392 of piezoelectric motor 390.

FIG. 12C shows a schematic side view along line A—A in FIG. 12B of ashaft 372 and driving arms 322 and 392 of piezoelectric motors 320 and390 respectively that drive the shaft. The side view schematically showssprings 526 and 534 that are supported respectively by brackets 524 and530. Springs 526 and 534 press on driving arm 392 of piezoelectric motor390 and exert forces between driving arms 32 and 392 that resilientlypress friction nubs 352 to coupling disc 374. A spring 536 betweendriving arms 322 and 392 that operates to press piezoelectric motor 320to pedestal 522 is also shown. Brackets 526 and 530 are cutaway to showfeatures that they would otherwise hide in the side view.

Whereas in FIGS. 11A–12C piezoelectric star motors 320 and 390 are shownhaving base plates 340 formed with holes 344 for receiving shafts (e.g.shafts 372 shown in FIGS. 11A, 11B–12C), as noted above, in somepiezoelectric star motors, the base plates are formed with slots forreceiving the shafts. In the case where base plates 340 are formed withslots, in some embodiments of the present invention, shafts driven bythe motors are, optionally, held in place by elastic elements.

FIG. 12D schematically shows a variation of piezoelectric motors 320 and390 shown in FIGS. 12A–12C in which base plates 340 of the motors areformed with slots 540 instead of with holes for holding shafts 372. Eachshaft 372 is preferably coupled to two ring bearings 542 spaced apartalong the shaft so that the shaft can be mounted to motors 320 and 390with a bearing 542 in each of slots 540 of driving arms 322 and 392 thatdrive the shaft. A spring 544 or other elastic element supported by anappropriate structure (not shown), which may, for example, be a frame towhich piezoelectric motors 320 and 390 are mounted, presses each ofbearings 542 into position in its respective slot 540 slot.

Springs 544 also function to damp longitudinal vibrations in drivingarms 392 and 322 of star motors 390 and 320 so that amplitudes of thelongitudinal vibrations do not exceed desired upper limits. Whereasdamping springs are shown for the variations of star motors 320 and 390shown in FIG. 12D, damping springs are used where advantageous in otherstar motors, in accordance with some embodiments of the presentinvention. Furthermore, whereas in FIG. 12D springs 544 damplongitudinal vibrations by pressing on bearings 542, in some embodimentsof the present invention, damping springs press directly on the ends ofthe arms of the piezoelectric vibrator and/or base plate in a star motorto damp longitudinal vibrations in the motor's driving arms.

When a shaft is driven by two piezoelectric motors, as in the examplesof embodiments of the present invention shown in FIGS. 12A–12D, totransfer energy from each of the motors to the shaft efficiently, it isadvantageous that both motors drive the shaft at substantially the samevelocity. For the star motor configurations shown in FIGS. 12A–12D, thisgenerally requires that friction nubs 352 of piezoelectric motors 320and 390 that transmit torque to a coupling disc 374 contact the couplingdisc at substantially a same radius. As noted above, piezoelectricmotors 320 and 390 are mirror images of each other. As a result,friction nubs 352 of piezoelectric motors 320 and 390 that contact asame coupling disc 374 are opposite each other and generally contact thecoupling disc at equal radii. However, as a result of wear, and/orvibrations and/or differences in dimensions and relative motion of partsdetermined by fabrication and assembly tolerances, friction nubs 352contacting a same coupling disc 374 can contact the coupling disc atdifferent radii or otherwise operate at different velocities.

FIG. 12E schematically shows piezoelectric star motors 320 and 390 shownin FIGS. 12A–12D coupled to drive shafts 372 via coupling discs 550 thatare constructed to reduce differences between radii at which frictionnubs 352 of the piezoelectric motors contact a same coupling disc. As inFIG. 12A, the foremost driving arm 392 of star motor 390, shaft 372 andcoupling disc 550 coupled to the foremost driving arms 392 and 322 ofstar motors 390 and 322 are partially cut away to reveal details ofcoupling of the motors to the coupling disc. Inset 552 in FIG. 12E showsa perspective view of a coupling disc 550 and a shaft 372 to which thecoupling disc is connected.

Coupling discs 550 are formed with a narrow raised circular ridge 554 oneach of its large surfaces 556. Ridges 554 of each coupling disc 550have substantially a same radius and are mirror images of each other inthe plane of the coupling disc 550. The radii of ridges 554 are suchthat friction nubs 352 of star motors 320 and 390 that rotate a samecoupling disc 554 seat on the disc's ridges. The widths of ridges 554are less than the width of friction nubs 352 of piezoelectric motors 320and 390. Therefore, as a friction nub 352 and/or ridge 554 of thecoupling disc 550 on which it seats wears, or as the friction nub movesslightly with respect to the annulus, the radius at which the frictionnub contacts the coupling disc remains substantially constant. As aresult, differences between radii at which friction nubs 352 of starmotors 320 and 390 contact a same coupling disc 550 are substantiallyreduced.

In addition to having friction nubs 352 of both star motors 320 and 390contact coupling discs that they drive at same radii it is alsoadvantageous for efficient operation of the motors that the vibrationmodes at which they operate have substantially a same frequency. In someembodiments of the present invention, a controller monitors and controlsdriving circuits that energize star motors 320 and 390, using methodsand devices known in the art, so that the driving circuits excite themotors at substantially a same frequency.

It is to be noted that an optimum resonant frequency for drivingdifferent star motors 320 and 390 can vary as a result of fabricationtolerances and wear of the motors. In some embodiments of the presentinvention, driving circuits that drive star motors 320 and 390 aredesigned, using methods and devices known in the art, to determine anoptimum frequency at which to drive the motors.

In some embodiments of the present invention, a same AC driving voltageexcites star motors 320 and 390. Therefore, friction nubs 352 on bothsides of each coupling disc 374 transmit torque simultaneously to thecoupling disc. Forces that one friction nub 352 exerts perpendicular tothe plane of a coupling disc 374 are therefore canceled by forcesexerted perpendicular to the plane of the coupling disc by the otherfriction nub 352. As a result, when two mirror image star motors areused to drive shafts 372, in accordance with an embodiment of thepresent invention, there is substantially no torque applied to thedisc's shaft 372 in a direction perpendicular to the shaft. Wear of thedisc, its shaft and bearings holding the shaft is thereby reduced.

In some embodiments of the present invention voltage applied to starmotor 320 is 180° out of phase with voltage applied to star motor 390(or polarization directions of the piezoelectric material in the starmotors are reversed relative to their respective structures and a sameAC voltage is applied to both motors). As a result, friction nubs 352 ofstar motors 320 and 390 coupled to a same coupling disc 374 alternatelycontact and transmit torque to the coupling disc. An advantage ofalternate transmission of torque to a coupling disc 374 is that torquetransmission is smoother than when torque is transmitted to the couplingdisc simultaneously by both motors.

FIG. 13A schematically shows a star motor 420, which is a variation ofstar motor 320. In star motor 420 edges of piezoelectric vibrator 330and base plate 340 of adjacent driving arms do not meet at sharplydefined corners as they do in star motor 320 but instead meet at roundedjunctions 421. Rounded junctions decrease stress in regions whereadjacent driving arms 322 meet and make it easier to polish and finishpiezoelectric vibrator 330.

In addition, driving arms 322 need not be rectangular but instead maytaper in width along their respective axes 324. For a given AC voltageand given thickness of driving arms 322, tapering amplifies amplitudesof motion of mass points at ends of driving arms 322 of star motor 420relative to amplitudes of corresponding mass points in driving arms 322of star motor 320. As a result, amplitudes of motion of friction nubs352 comprised in star motor 420 are amplified with respect to amplitudesof motion of friction nubs 352 comprised in star motor 320.

In some embodiments of the present invention thickness of piezoelectricvibrator 330 and/or base plate 340 decreases with distance from center326 of star motor 420 along axes 324. As in the case of tapering,decrease in thickness of piezoelectric vibrator 330 and/or base plate340 along axes 324 results in amplified motion of friction nubs 352. (Itis to be noted that tapering or thinning a driving arm will generally,for a given voltage, reduce maximum force provided by the driving arm.)

In star motors 320 and 420 shown in FIGS. 11A–13A, bending vibrations ofdriving arms 322 are generated by mechanical stress between a layer ofpiezoelectric material driven to expand and contract by an electricfield and a passive layer of material that is not excited by theelectric field. In star motors in accordance with some embodiments ofthe present invention other methods are used to generate bendingvibrations in driving arms of the motors.

In accordance with some embodiments of the present invention a starmotor comprises a plurality of layers of piezoelectric material andbending vibrations in driving arms of the motor are generated byelectrifying appropriate electrodes on layers of the motor.

FIG. 13B schematically shows an example of a star motor 422, inaccordance with an embodiment of the present invention, comprising twolayers of piezoelectric material, a top layer 423 and a bottom layer424. Electrodes on surface regions of the motor and sandwiched betweenlayers 423 and 424 are electrified to generate bending vibrations indriving arms 322 of the motor.

Star motor 422, by way of example, has a shape similar to that of starmotor 420 and is formed with tapering driving arms 322 and roundedjunctions 421 between adjacent driving arms 322. Optionally, a singlelarge “central” electrode 425, only an edge of which is shown in FIG.13B, is sandwiched between top and bottom piezoelectric layers 423 and424. In some embodiments of the present invention, bottom piezoelectriclayer 424 is a mirror image in the plane of central electrode 425 of toppiezoelectric layer 423. Top piezoelectric layer 423 optionally has asingle large electrode 426 on a surface 427 thereof and bottompiezoelectric layer 424 has a corresponding “mirror image electrode”(not shown) on a surface 428 of the bottom piezoelectric layer. Assume,by way of example, that polarization directions of the two piezoelectriclayers 423 and 424 are perpendicular to central electrode 425 and pointin opposite directions (which, for perpendicular polarization directionsfollows from layers 423 and 424 being mirror images of each other).

In accordance with an embodiment of the present invention, to generatevibrations in friction nubs 352 of star motor 422 useful fortransmitting motion to a moveable element, a first AC voltage differenceis applied between central electrode 425 and electrode 426. A secondvoltage difference having a same frequency and phase but differentamplitude as the first voltage difference is applied between centralelectrode 425 and the mirror image electrode on surface 428 ofpiezoelectric layer 424. The applied voltage differences generatelongitudinal and bending vibrations in driving arms 322 that result inelliptical vibrations of friction nubs 352 suitable for transmittingmotion to moveable elements.

FIG. 13C schematically shows an example of a star motor 480 inaccordance with an embodiment of the present invention in whichasymmetries in the mass distributions of driving arms 322 generatebending vibrations in the driving arms.

Star motor 480 comprises a single piezoelectric vibrator 482 having ashape, by way of example, similar to that of piezoelectric vibrator 330comprised in star motor 320, which is shown in FIG. 11A–12A. Star motor480 optionally has a single large electrode 484 on a top surface 486 ofthe motor and optionally an identical electrode (not shown) on a bottomsurface 488 of the motor. Each driving arm 322 has a mass element 490affixed to the driving arm on face surface 486. Mass element 490 breakssymmetry of the mass distribution of the driving arm about a plane (notshown) though the center of the driving arm parallel to surface 486.

When an AC voltage is applied between electrode 484 and the electrode onsurface 488 of star motor 480, a longitudinal vibration is excited ineach driving arm 322 of the motor. Forces generated by the longitudinalvibration that accelerate mass element 490 of the driving arm 322generate torque on the driving arm that excites a bending vibration modein the driving arm. In some embodiments of the present invention, masselement 490 of each driving arm is located at an antinode of thelongitudinal vibration excited in the driving arm.

In some star motors, in accordance with embodiments of the presentinvention, forces between friction nubs of driving arms of the motorsand moveable elements that the driving arms move generate bendingvibrations in the driving arms. When the friction nub of a driving armtransmits motion to a moveable element it applies a force to the elementthat is parallel to the plane of the driving arm. A reaction force equaland opposite to the force applied to the moveable element by thefriction nub operates on the friction nub. Since the contact pointbetween the friction nub and the moveable element is displaced from theplane of the driving arm, the reaction force generates a torque thatbends the driving arm and excites a bending vibration in the drivingarm.

FIG. 14A schematically shows another star motor 400 in accordance withan embodiment of the present invention.

Star motor 400 is similar to star motor 320. However, unlike star motor320, star motor 400 has two friction nubs 352 on each driving arm 322and instead of a single large electrode 60 (FIGS. 11A and 11C) coveringface surface 332 of piezoelectric vibrator 330 the star motor has threeelectrodes 402. One electrode 402 is located in a region of face surface332 of each driving arm 322. In some embodiments of the presentinvention, each electrode 402 runs substantially the length of thedriving arm 322 on which it is located and covers substantially one halfof the surface area 332 of the arm on one side of axis 324. In someembodiments of the present invention, electrodes 402 are located on asame side of axes 324 of their respective driving arms 322. In FIG. 14A,by way of example, electrodes 402 are located on the left sides of theirrespective axes 324 as seen from center 326 of star motor 400.

When an AC voltage difference is applied between electrode 402 of adriving arm 322 and base plate 340, the voltage difference generates alongitudinal vibration in the arm parallel to axis 324 of the arm and atwisting vibration of the arm about the axis. The twisting vibrationcyclically moves one friction nub 352 of the driving arm 322 up and downwhile moving the other friction nub 352 respectively down and up alongdirections perpendicular to the plane of the driving arm. Friction nubs352 execute a seesaw motion with respect to each other about axis 324 ofthe driving arm. In some embodiments of the present invention allelectrodes 402 are electrically connected.

The up and down motion of the twisting vibration and the back and forthmotion of the longitudinal vibration cause each friction nub 352 tovibrate with an elliptical motion. The elliptical motion of eachfriction nub 352 for the foremost driving arm 322 in FIG. 14A isschematically represented by an ellipse 404 located near the frictionnub. Since one friction nub 352 moves up while the other moves down, thefriction nubs “move around” their respective ellipses 404 in a samesense, as seen from a point on axis 324 located between the frictionnubs. In FIG. 14A both friction nubs move counterclockwise. Direction ofmotion of friction nubs 352 about their respective ellipses 404 areindicated by curved arrows 406. It should be noted that were electrodes402 to be located on the right sides of their respective driving arms322, they would move clockwise around their ellipses 404.

Star motor 400 is coupled to shafts of the type shown in FIGS. 11A–12Asimilarly to the manner in which star motor 320 is coupled to theshafts. A shaft 372 is positioned to pass through a clearance hole 344of a driving arm 322 of motor 400 so that the shaft's coupling disc 374is resiliently pressed to both friction nubs 352 of the driving arm.When the driving arm 322 is excited to vibrate by an AC voltage, duringeach vibration cycle of the driving arm each friction nub 352alternately contacts coupling disc 374 and transmits torque to the disc.For the configuration of electrodes 402 shown in FIG. 14A, driving arms322 of star motor 400 drive shafts 372 counterclockwise.

As in the case of star motor 320, one or two star motors 400, inaccordance with embodiments of the present invention, are used to drivethree shafts 372. FIG. 14B schematically shows a single star motor 400coupled to drive three shafts 372 connected to rotary shaver blade heads380, in accordance with an embodiment of the present invention.Direction of rotation of shafts 372 and rotary blade heads 380 are shownby curved arrows 408. It is to be noted that were electrodes 402 locatedon sides of their respective driving arms opposite to the sides on whichthey are shown in FIGS. 14A and 14B shafts 372 would be drivenclockwise.

In some configurations of star motor 400, dimensions and material of themotor are chosen so that a frequency of a resonant bending vibrationmode of driving arms 322 of the motor is close to a frequency of aresonant transverse vibration mode of the driving arms. The bending andtransverse vibration modes generate motion of friction nubs 352 that areuseful for rotating a moveable element.

The bending mode of a driving arm 322 is a bending mode perpendicular tothe plane of the driving arm, i.e a bending mode similar to bendingmodes described above. The transverse mode is an “in-plane” vibrationmode that causes bending of the driving arm 322 in the plane of thedriving arm. The bending mode and transverse mode are both excited whenthe longitudinal vibration mode is excited. The bending mode moves bothfriction nubs 352 of the driving arm 322 up and down perpendicular tothe plane of the driving arm together so that both friction nubssimultaneously contact a surface of a moveable element being moved bythe driving arm. However, the transverse mode moves friction nubs 352back and forth in opposite directions about centerline 346 of hole 344of the driving arm, i.e. friction nubs 352 “seesaw” about centerline 346rather than axis 324. Therefore, when the two friction nubs contact theelement being moved they generate a torque couple on the element thatoperates to rotate the element about centerline 346.

FIG. 14C schematically shows another star motor 560, in accordance withan embodiment of the present invention. Star motor 560 is similar tostar motor 400 except that instead of a single rectangular electrode 402on a region of face surface 330 of each driving arm 322, each drivingarm has four quadrant electrodes 561, 562, 563 and 564. All evennumbered electrodes 562 and 564 are connected together and all oddnumbered electrodes 561 and 563 are connected together. When evennumbered electrodes 562 and 564 are grounded or floating and oddnumbered electrodes 561 and 563 are electrified with an appropriate ACexcitation voltage, friction nubs 352 vibrate with elliptical motionsindicated by ellipses 404. Friction nubs 352 “move around” theirrespective ellipses 404 in directions indicated by arrows 406. As aresult, when odd numbered electrodes 562 and 564 are excited by the ACexcitation voltage, shafts (not shown) coupled to driving arms 322 byappropriate coupling discs are rotated clockwise (as in FIG. 14B). Whenodd numbered electrodes 561 and 563 are grounded or floating, and evennumbered electrodes 562 and 564 are excited by the AC voltage, frictionnubs 352 execute vibratory motion indicated by the same ellipses 404.However, in this case the friction nubs move around their respectiveellipses in directions opposite to directions indicated by arrows 406.As a result, when odd numbered electrodes 561 and 563 are excited,shafts driven by star motor 560 are rotated counterclockwise by the starmotor. It is to be noted that whereas FIGS. 11A–14B show starpiezoelectric motors having three driving arms, star motors, inaccordance with embodiments of the present invention can have other thanthree driving arms. FIGS. 15A and 15B schematically show, by way ofexample, star motors 430 and 432 having respectively two and fourdriving arms 322. Motors 430 and 432 and variations of the motorssimilar to variations of motors shown in FIGS. 11A–13 are operated torotate two and four shafts respectively similarly to the way in whichthe three armed motors are operated to drive three shafts. FIG. 16schematically shows, a configuration in which two “mirror image” starmotors, 440 and 442 of a type show in preceding figures, each comprisingthree driving arms, are used to drive three rotary shaver blade heads380. Each of the three blade heads 380 is coupled to a shaft 444 that ismounted to coupling discs 446 which are also gears. Shafts 444 and theirrespective coupling discs 446 are coupled to friction nubs (not shown)of star motors 440 and 442 in a manner described above and are directlydriven by vibrations in driving arms 322 of the motors. Disc-gears 446are coupled to a common gear 450 mounted to a shaft 448 that passesthrough the centers of star motors 440 and 442. As a result of couplingdisc-gears 446 to a same gear 450 motion of the disc-gears issynchronized and substantially a same amount of power from motors 440and 442 is coupled to all shafts 444 and their corresponding rotaryblade heads 380.

FIG. 17 schematically shows an example of another star motor 452, inaccordance with an embodiment of the present invention, which is formedfrom a single relatively thin layer 452 of piezoelectric material havinga top face surface 454 and a bottom face surface 456. Piezoelectriclayer 452 is formed, by way of example, with three rectangular drivingarms 322. In some embodiments of the present invention, two electrodes,459 and 460, are located on a region of top face surface 454 of eachdriving arm 322. Electrode 459 of a driving arm 322 optimally coverssubstantially half of surface 454 in the region of the driving arm tothe left of axis 324 of the driving arm as seen from center 326 of starmotor 450. Electrode 460 covers substantially a left half of the regionof surface 454 in the region of the driving arm. A single largeelectrode (not shown) covers substantially all the surface area of facesurface 456. A friction nub 460 is located on an “end” edge surface 462of each driving arm 458.

In some embodiments of the present invention all “right-hand” electrodes460 are electrified simultaneously with respect to the large electrodeon face surface 456 with a same AC voltage. All left-hand electrodes 459are simultaneously electrified with respect to the large electrode withan AC voltage 180° out of phase with the AC voltage that electrifies theright hand electrodes 460. The applied voltages generate longitudinaland transverse vibration modes in each driving arm 322 that generateelliptical vibrations in friction nub 460 of the driving arm.

In some embodiments of the present invention, the elliptical vibrationsare used to rotate a shaft. In FIG. 17 star motor 450 is shown coupledto three rotary blade heads 380, each of which is mounted on a shaft 464having a coupling wheel 466. A friction nub 460 of each driving arm 322is resiliently pressed to a coupling wheel 466 of a shaft 464 andelliptical vibrations of the friction nub rotate the coupling wheel.

It should be noted that whereas each driving arm 322 of star motor 450has two electrodes located on its region of surface 454 otherconfigurations of electrodes for driving arms 322 can be used. Forexample, in some embodiments of the present invention each driving arm322 has an electrode configuration of four quadrant electrodes similarto that shown for piezoelectric motor 20 shown in FIG. 1A or anelectrode configuration similar to that of piezoelectric motor 56 alsoshown in FIG. 1A.

It should also be noted that frequencies of resonant vibration modes ofdriving arms of star motors, in accordance with embodiments of thepresent invention, can be adjusted by forming holes or grooves in thepiezoelectric layer of the driving arms. The use of holes and grooves toadjust resonant frequencies of piezoelectric motors is described in PCTapplication PCT/IL00/00116, the disclosure of which is incorporatedherein by reference. The use of holes and grooves for adjusting resonantfrequencies of a motor similar to motor 20 is discussed above, forexample in the discussions that reference FIGS. 1A and 1C In thedescription and claims of the present application, each of the verbs,“comprise” “include” and “have”, and conjugates thereof, are used toindicate that the object or objects of the verb are not necessarily acomplete listing of members, components, elements or parts of thesubject or subjects of the verb.

The present invention has been described using detailed descriptions ofembodiments thereof that are provided by way of example and are notintended to limit the scope of the invention. The described embodimentscomprise different features, not all of which are required in allembodiments of the invention. Some embodiments of the present inventionutilize only some of the features or possible combinations of thefeatures. Variations of embodiments of the present invention that aredescribed and embodiments of the present invention comprising differentcombinations of features noted in the described embodiments will occurto persons of the art. The scope of the invention is limited only by thefollowing claims.

1. A piezoelectric motor comprising: a layer of piezoelectric material having narrow edge surfaces and first and second large face surfaces, formed with at least three arms, each extending radially outward from a common central region and terminating in an end; at least one electrode on the first surface and at least one electrode on the second face surface; and an AC voltage source connected to the at least one electrode on the first surface and at least one electrode on the second surface that electrifies the electrodes and generates thereby vibratory motion in mass points in a neighborhood of the end of each arm that has at least a component of vibration perpendicular to the plane of the arm.
 2. A piezoelectric motor according to claim 1 wherein each arm has a bilateral axis of symmetry that extends from the central region.
 3. A piezoelectric motor according to claim 2 wherein each of the arms of the piezoelectric layer is substantially rectangular.
 4. A piezoelectric motor according to claim 2 wherein each of the arms is substantially trapezoidal with its width decreasing with distance from the central region.
 5. A piezoelectric motor according to claim 3 wherein the thickness of each piezoelectric arm decreases with distance from the central region.
 6. A piezoelectric motor according to claim 3 wherein junctions of an arm with the central region are curved.
 7. A piezoelectric motor according to claim 1 and comprising a mass element affixed to each arm on the first surface at a distance from the central region and wherein when longitudinal vibrations are excited in the arm the mass generates a torque that excites bending vibrations in the arm.
 8. A piezoelectric motor according to claim 2 and comprising a thin plate having two large face surfaces and at least three arms, said plate being substantially similar in shape to the piezoelectric layer, wherein the first face surface of the piezoelectric layer is aligned with and bonded to one of the face surfaces of the plate.
 9. A piezoelectric motor according to claim 8 wherein the thin plate is formed from a non-piezoelectric material.
 10. A piezoelectric motor according to claim 9 wherein the material is non-conductive.
 11. A piezoelectric motor according to claim 10 wherein the at least one electrode on the first face surface of the piezoelectric layer comprises a single large electrode covering substantially the entire first surface.
 12. A piezoelectric motor according to claim 9 wherein the material is a conductor.
 13. A piezoelectric motor according to claim 8 and comprising a mass element affixed to each arm on the first surface at a distance from the central region and wherein when longitudinal vibrations are excited in the arm the mass generates a torque that excites bending vibrations in the arm.
 14. A piezoelectric motor according to claim 7 wherein the at least one electrode on the second face surface of the piezoelectric layer comprises a single large electrode covering substantially the entire second surface.
 15. A piezoelectric motor according to claim 8 wherein the at least one electrode on the second face surface comprises a single electrode on each arm that covers substantially all the area of the second surface on one side of the arm's axis of symmetry and substantially none of the area on the other side.
 16. A piezoelectric motor according to claim 15 wherein the single electrode on any one arm is homologous with the single electrode on any of the other arms.
 17. A piezoelectric motor according to claim 16 wherein the electrodes on the second face surface are electrically connected.
 18. A piezoelectric motor according to claim 8 wherein the at least one electrode on the second face surface comprises first and second separate electrodes on each arm that are located on opposite sides of the arm's bilateral axis of symmetry and together cover substantially all the area of the second surface in the region of the sum.
 19. A piezoelectric motor according to claim 18 wherein the first and second electrodes on any one arm are homologous respectively with the first and second electrodes on any of the other arms and all the first electrodes are connected to form a first set of electrodes and all the second electrodes are connected to form a second set of electrodes.
 20. A piezoelectric motor according to claim 19 wherein the source of voltage electrifies the first and second electrodes with respect to at least one electrode on the first surface with first and second AC voltages respectively that are 180° out of phase so that mass points near opposite corners of the end of each arm execute same sense elliptical vibratory motion as seen from a point on the bilateral axis of symmetry of the arm.
 21. A piezoelectric motor according to claim 8 wherein the at least one electrode on the second face surface of the piezoelectric layer comprises four electrodes one each arm that are arranged in a checkerboard pattern with each electrode located in a different quadrant of the second surface in the region of the arm.
 22. A piezoelectric motor according to claim 21 wherein diagonally opposite electrodes on each arm are electrically connected to form a first and second pair of diagonally connected electrodes on each arm and wherein first and second pairs of diagonal electrodes on each arm are homologous respectively with the first and second diagonal pairs of electrodes on any of the other arms of the motor.
 23. A piezoelectric motor according to claim 22 wherein all the first diagonal pairs of electrodes are electrically connected to form a first set of diagonal electrodes and all the second pairs of diagonal electrodes are electrically connected to form a second set of diagonal electrodes.
 24. A piezoelectric motor according to claim 23 wherein the AC electrifies the first set of diagonal electrodes with resect to the at least one electrode on the first surface while the second set of diagonal electrodes is grounded or floating, so that mass points in opposite corners of the end of each arm execute clockwise elliptical vibratory motion perpendicular to the plane of the motor as seen from a point on the bilateral axis of symmetry of the arm.
 25. A piezoelectric motor according to claim 23 wherein the AC voltage source electrifies the second set of diagonal electrodes with respect to the at least one electrode on the first surface while the first set of diagonal electrodes is grounded or floating, so that mass points in opposite corners of the end of each arm execute counterclockwise elliptical vibratory motion perpendicular to the plane of the motor as seen from a point on the bilateral axis of symmetry of the arm.
 26. A piezoelectric motor according to claim 14 wherein the at least one electrode on the first face surface comprises a single large electrode covering substantially the entire first face surface.
 27. A piezoelectric motor according to claim 2 wherein the at least one electrode on the first surface is a first electrode covering substantially all the area of the first surface and the at least one electrode on the second surface is a second electrode covering substantially all the area of the second surface and comprising: an additional layer of piezoelectric material having first and second large face surfaces having a shape substantially the same as the shape of the first surface of the piezoelectric layer located between the first and second electrodes and wherein the first surface of the additional layer is bonded to the first surface of the piezoelectric layer located between the first and second electrodes; and a third electrode covering substantially all of the second surface of the additional layer.
 28. A piezoelectric motor according to claim 27 wherein the additional layer is a mirror image of the piezoelectric layer.
 29. A piezoelectric motor according to claim 28 wherein the source of AC voltage connected to the first, second and third electrodes electrifies the first and third electrodes with respect to the second electrode with AC voltages having a same frequency and phase but different amplitudes.
 30. A piezoelectric motor according to claim 27 wherein the piezoelectric layer between the first and second electrodes and the additional layer have different thicknesses.
 31. A piezoelectric motor according to claim 30 wherein the source of AC voltage electrifies first and third electrodes with respect to the second electrode with a same AC voltage.
 32. A piezoelectric motor according to claim 1 and comprising a friction nub located on the edge surface of the end of each piezoelectric arm.
 33. A piezoelectric motor according to claim 2 and comprising a friction nub located on the second surface of the piezoelectric layer near a corner of the end of each piezoelectric arm.
 34. A piezoelectric motor according to claim 8 and comprising on the surface of the thin plate that is not bonded to the piezoelectric layer a friction nub located near a corner of the end of each arm of the plate.
 35. A piezoelectric motor according to claim 2 and comprising an extension for each arm formed from a non-piezoelectric material that is bonded to the end of the arm, which extension comprises a friction nub located on a surface of the extension that is parallel to the plane of the arm and displaced from the bilateral axis of symmetry.
 36. A piezoelectric motor according to claim 2 and comprising two substantially identical friction nubs located on the second surface in opposite corners of the end of each piezoelectric arm and wherein a straight line connecting the friction nubs is substantially perpendicular to the bilateral axis of symmetry of the arm.
 37. A piezoelectric motor according to claim 8 and comprising, on the surface of the plate not bonded to the piezoelectric layer, two substantially identical friction nubs located near corners of the end of each arm of the plate and wherein a straight line connecting the friction nubs is substantially perpendicular to the bilateral axis of symmetry of the arm.
 38. A piezoelectric motor according to claim 8 and comprising an extension for each arm formed from a non-piezoelectric material that is bonded to the end of the arm, which extension comprises a friction nub on each side of the bilateral axis of symmetry of the arm and wherein a straight line connecting the friction nubs is substantially perpendicular to the bilateral axis of symmetry.
 39. A piezoelectric motor according to claim 33 and comprising a disc, having an axis of rotation perpendicular to surfaces thereof, mounted to the friction nub of each arm, wherein the axis of rotation is perpendicular to the plane of the arm and the friction nub contacts a disc surface at a point on the disc surface for which a line from the point perpendicular to the axis of rotation is substantially perpendicular to the bilateral axis of the arm.
 40. A piezoelectric motor according to claim 39 wherein the axis of rotation intersects the bilateral axis of the symmetry of the arm.
 41. A piezoelectric motor according to claim 36 and comprising a disc, having an axis of rotation perpendicular to surfaces thereof, for each arm, wherein a surface of the disc is resiliently pressed to both friction nubs of the arm and the disc's axis of rotation is perpendicular to and passes through the arm's bilateral axis of symmetry and the line connecting the friction nubs.
 42. A motor according to claim 1 wherein the piezoelectric motor has a rotational symmetry of order equal to the number of arms in the motor.
 43. A compound piezoelectric motor comprising: first and second mirror image piezoelectric motors according to claim 33 having the axes of symmetry of their respective arms parallel and friction nubs facing each other; a disc, having an axis of rotation perpendicular to surfaces thereof positioned between each arm of the first piezoelectric motor and its mirror image arm in the second piezoelectric motor, wherein the disc's axis of rotation is perpendicular to the bilateral axes of symmetry of the mirror image arms and each of the friction nubs of the arms is in contact with one of the disc surfaces; and at least one elastic element that resiliently presses the first and second piezoelectric motors towards each other so that each of the friction nubs of the motors is resiliently pressed to the disc surface that it contacts.
 44. A compound piezoelectric motor according to claim 39 wherein the disc surface is formed with a thin circular ridge having a center located on the axis of revolution of the disc and wherein the friction nub contacts the surface contacts the ridge.
 45. A piezoelectric motor according to claim 39 wherein the discs are formed as gears and the motor comprises a gear mounted to the central region of the motor which meshes with all the discs.
 46. A piezoelectric motor according to claim 39 wherein each of the discs is formed with an edge surface and the motor comprises an additional disc having an edge surface which is mounted to the central region of the motor so that the edge surface of the additional disc is in frictional contact with the edge surface of each of the other discs.
 47. A piezoelectric motor according to claim 39 wherein each disc is mounted with a shaft having an axis of rotation coincident with the disc's axis of rotation.
 48. A piezoelectric motor according to claim 39 wherein the discs are mounted integrally to the body of the motor.
 49. A shaver comprising a motor according to claim 48 wherein each shaft is mounted with a blade head having an axis of rotation coincident with the axis of the shaft and at least one cutting blade having a cutting edge for cutting hair that extends substantially radially away from the blade head's axis of rotation.
 50. A compound piezoelectric motor comprising: first and second mirror image piezoelectric motors according to claim 36 having the axes of symmetry of their respective arms parallel and friction nubs facing each other; a disc, having an axis of rotation perpendicular to surfaces thereof positioned between each arm of the first piezoelectric motor and its mirror image arm in the second piezoelectric motor, wherein the disc's axis of rotation is perpendicular to the bilateral axes of symmetry of the mirror image arms and each of the friction nubs of the arms is in contact with one of the disc surfaces; and at least one elastic element that resiliently presses the first and second piezoelectric motors towards each other so that each of the friction nubs of the motors is resiliently pressed to the disc surface that it contacts.
 51. A compound piezoelectric motor according to claim 50 wherein each disc surface is formed with a thin circular ridge having a center located on the axis of revolution of the disc and wherein each of the friction nubs of the piezoelectric motor that contacts the surface contacts the ridge. 